How to divide a mortgage and living area fairly?
I suggest that you first decide on what %'s of the home value you each have a legal claim to. Then split the mortgage using the same %'s. Then, if someone feels their % is slightly higher, they are compensated because they 'own' a correspondingly higher share of the house. Use the same %'s for downpayments (which may mean that an 'adjustment' payment might be required to bring your initial cash outlay from 70/30 into the %'s that you agree to). Tenant income gets split the same way. Utilities are a bit more difficult - as heating depends more on square feet, but water and hydro depend more on how many people are there. You can try to be really precise about working out the %'s, or just keep it simple by using the same %'s as the mortgage. In my opinion, since she will live in one apartment, as will you and your husband, the simplest method is to divide the ratio exactly the same as the area for your living space. If it's 40/60, she puts 40% down, you put 60%. And you split expenses the same.  The tenant income can be applied to the house expenses, as it's no different than giving her 40% and you keep 60%.  No matter how well you get along, it's easy for someone to feel a split of expenses isn't fair unless it's discussed and agreed up front. I think what you have here is actually TWO agreements with your sister, and explicitly splitting it into two agreements will bring some clarity. The first is ownership of and responsibility for the building. The second is each of your personal use of a unit.  Here's what you do: Treat ownership as if you're not living there. Split the down payment, the monthly mortgage, taxes and insurance, responsibility for cost of maintenance, etc. as well as the ownership and benefit of the building 70%/30%. Put all that in a contract. Treat it like a business. Second, lease those units to yourselves as if you were tenants. And yes, I means even with leases. This clarifies your responsibilities in a tenant capacity. More to the point, each of you pays rent at the going rate for the unit you occupy.   If rent from all three units equals the monthly expenses, nothing more needs to be done. If they're more than the monthly expenses, then each of you receives that as business income on that 70%/30% breakdown. If those three rents are less than the monthly expenses, then each of you are required to make up the difference, again at 70%/30%.  Note: if any of those expenses are utilities, then they should be apportioned via the rent -- just as you would if you'd rented out the whole building to strangers.  2nd note: all that can be done with ledger entries, rather than moving money around, first as rent, then as expense payments, then as payouts. But, I think it will benefit all of you to explicitly pay rent at first, to really clarify your dual relationship as joint owners and as tenants.  Final note: I think this is a stickier situation than you may think it is. Familial relationships have been destroyed both by going into business together, and by renting to family members. You're doing both, and mixing the two to boot. I'm not saying it will destroy your relationship, but that there's a solid risk there. Relationship destruction comes from assumptions and vague verbal agreements. Therefor, for the sake of all of you, put everything in writing. A clear contract for the business side, and clear leases for the tenant side. It's not about trust -- it's about understood communication and positive agreement on all important points.
I don't like it using percentages makes no sense.  Find out what market value is for rent and pay 1/2 of that to your partner, adjust annually.   You partner should be protected from inflation if he is going to invest in real estate. "Have her chip in for the regular expenses, utilities, food, etc., and a bit for ""rent."" Then tell her to be sure to deposit to her retirement account, preferably a matched 401(k).  It's admirable to want her to build 'equity' but it's pretty convoluted. You can't actually give her ownership, and in the event you break up (I know you won't, but this is to help other readers) you'll have to pay her back a lump sum when she moves out. That might not be so easy." I don't think there's a conclusive answer to your question, but I have a real world example for you.   I was in a similar situation for almost 6 years (I was the friend, but also the one with the highest pay). I rented a house, my name on everything. I made a separate contract with both my friend and his GF and they both rented a room from me. I looked up the total m2 of the house and divided the rent by that number. Multiplied by room sizes I knew what everyone had to pay for their personal space, I simply divided the rest by 3 to find the remainder of everyone's rent.   I don't know the numbers anymore, but here's an example: house = 150 m2 room 1 = 10 m2 room 2 = 15 m2 room 3 = 25 m2 shared space = 100 m2 rent = 800,-   This gives 5.33 per m2 The shared space is worth 533.33 Divided by 3 is 177.77, So the total rent for each room is: room 1 = 10*5.33 + 177.77 ≈ 231 room 2 = 15*5.33 + 177.77 ≈ 258 room 3 = 25*5.33 + 177.77 ≈ 311   We divided the rest of the costs (gas, power, water, etc...) evenly. This was fair in our case, because the rent was directly tied to the size of the rooms. The only thing we had left to do was give the poorest person the smallest room. Is she entitled to more of the equity because she made more? No.  Equity should be determined by how much each paid.  But she is entitled to more of the equity if she paid more.  And that may be what she is saying.  That she contributed more to the household's finances than you did.   If you always paid the mortgage out of the joint account, you could presumably go back and look at the account to find out how much each of you contributed to it.  That would give you a reasonable split for the remainder of the equity after your initial investment.  If you both put your entire paychecks into the joint account every time, then it will be the same as the ratio of what you each made.  That would also make sense for splitting up whatever remains in that account.   While you're doing that, you may want to ask for more for your original $65,000.  By my calculation, if your mortgage was 3.5%, that $65,000 saved the household more than $12,000 in interest that became equity instead.  So you could reasonably bump your return on the initial investment up to $77,000 while making the concession on the rest of the equity.   This is just a suggestion for a framework for splitting the equity.  If you can agree on a split, it will almost certainly be easier than going to a mediator or court. "The New York Times offer a remarkably detailed Buy vs Rent calculator.  You enter - From all of this, it advises the break-even rent, when monetarily, it's equal.  I'd suggest you keep a few things in mind when using such a tool. Logic, common sense, and a Nobel prize winner named Robert Shiller all indicate that housing will follow inflation over the long term. Short term, even 20 years, the graphs will hint at something else, but the real long term, the cost of housing can't exceed inflation.  The other major point I'd add is that I see you wrote ""We rent a nice house."" Most often, people are looking to buy what they feel they can't easily rent. Whether it's the yard, room number or sizes, etc. This also leads to the purchase of too big a house. You can find that you can afford the extra bedroom, family room in addition to living room, etc, and then buy a house 50% bigger than what you need or planned on. In my opinion, getting the smallest house you can imagine living in, no bigger than what you live in now, and plan to get on a faster than 30 year repayment. Even with transaction costs, in 10 years, you'll have saved enough to make the bump up to a larger house if you wish." First, this was never an arrangement for you to build equity, this was an arrangement for them to speculate on another house under the guise of teaching you a life lesson like responsibility or something contrived. The only way you profit from this is if the value of the house goes up and you sell it. You get 25% of the proceeds, maybe. If this was an equitable arrangement then they would be paying 75% of the property taxes and a little more for your maintenance efforts. If there was no question of improvements to the property, the problem would be simple. Each person invests whatever amount. Calculate the percentage of each person's investment out of the entire investment, and that's what share each one owns. Like: A puts in $10,000 for the deposit and pays $5,000 toward the mortgage over the next however many years. B puts in $5,000 toward the deposit but pays $7,000 of the mortgage. C puts in $15,000 but pays only $1,000 of the mortgage payments. So total investments: A - $15,000, B - $12,000, C - $16,000. Total - $43,000. So A's share of the house is 15,000/43,000 = 34.9%. Etc. If you then sell it you pay off any outstanding debt, and then everybody gets their share of what's left. But once you start making improvements, there is no simple formula. Suppose you put down new flooring in the dining room. You pay $500 for materials and put in 20 hours of labor. Presumably you have now added something more than $500 to your share, but how much more? How much are the hours worth? What if someone damages the house -- puts a hole in the all or something -- and then fixes it. Does the time and effort they put into fixing it add to their investment, or did that just cancel out the damage they did? What if one person does a lot to keep the house in generally good condition in small snippets of time, like cleaning furnace filters and polishing the floors, while another does nothing and lets their share get run down and dirty? It gets very complicated. Theoretically you could come up with a rate at which you value your work -- like say every hour spent maintaining the house is worth $10 or $20 or whatever. But who's going to keep track of it over the course of potentially many years? And what if one person does a small number of big, easily quantifiable jobs, while another does many small, hard-to-count jobs? Like if A mops the floor every week for 2 years, is that worth more or less than B installing 3 ceiling fans, a door, and 2 windows? You could go around and around on this sort of thing. New York City is high cost-of-living, and I have absolutely no clue why people live there.  It's a tough place, and the taxes are oppressive.  People buy a studio apartment for $150,000 that has 175 square feet (that's not a typo) plus a $700/month maintenance fee that continues after the mortgage is paid off.  And that's just what the fee is now. Our rental house (which used to be our primary residence) at 1,300 square feet has a (15-year) mortgage payment of about $800, and $1,000 per year in property taxes.  And my area isn't particularly low cost-of-living. High cost-of-living is just that.  More money flies out the door just for the privilege of living there.  You make good investments with real estate by buying property at a good price in a good location.  Those deals are everywhere, but in high CoL locations you're probably more susceptible to price fluctuations which will trap you in your property if your mortgage goes underwater. Anyway, that's a long way of saying that I don't buy your recommendation to get property in high CoL areas.  There are desirable low CoL places to live, too. No. This logic is dangerous.  The apples to apples comparison between renting and buying should be between similar living arrangements. One can't (legitimately) compare living in a 600 sq ft studio to a 3500 sq ft house.  With the proposal you offer, one should get the largest mortgage they qualify for, but that can result in a house far too big for their needs. Borrowing to buy just what you need makes sense. Borrowing to buy a house with rooms you may never visit, not a great idea.  By the way, do the numbers. The 30 year rate is 4%. You'd need a $250,000 mortgage to get $10,000 in interest the first year, that's a $312,000 house given an 80% loan. On a median income, do you think it makes sense to buy a house twice the US median?  Last, a portion of the tax savings is 'lost' to the fact that you have a standard deduction of nearly $6,000 in 2012. So that huge mortgage gets you an extra $4000 in write-off, and $600 back in taxes.  Don't ever let the Tax Tail wag the Investing Dog, or in this case the House Dog.  Edit - the investment return on real estate is a hot topic. I think it's fair to say that long term one must include the rental value of the house in calculating returns. In the case of buying of way-too-big house, you are not getting the return, it's the same as renting a four bedroom, but leaving three empty.  If I can go on a bit - I own a rental, it's worth $200K and after condo fee and property tax, I get $10K/yr. A 5% return, plus whatever appreciation. Now, if I lived there, I'd correctly claim that part of my return is the rental value, the rent I don't pay elsewhere, so the return to me is the potential growth as well as saved rent. But if the condo rents for $1200, and I'd otherwise live in a $600 apartment with less space, the return to me is lost. In my personal case, in fact, I bought a too big house. Not too big for our paycheck, the cost and therefore the mortgage were well below what the bank qualified us for. Too big for the need. I paid for two rooms we really don't use. The simplest way to handle this is for you to rent the apartment and sublet to the girlfriend and friend.  I'd split the utilities evenly, one-third from each.  The reason for this is that each of you contribute evenly to generating the utility bills.  It's not like your income makes the water cost more for you.   Utilities are driven by usage.  Dividing them other than equally is likely to lead to more problems than it solves.  Also, it seems unlikely that a different apartment would use significantly different water, electricity, or internet.  Those are driven by the appliances rather than the size or location of the apartment.  Only pay more for the utilities if you want something that they don't.  For example, maybe you want HBO, etc.  It would be reasonable for you to pay the entire premium if that's a luxury that they simply wouldn't buy.   I'd also divide the groceries evenly if you share and share alike.  If you eat separate meals, you can buy separate groceries.   If the rent can't be split evenly but you could afford it alone, then you can just sign up for it.  If you break up with the girlfriend and/or the friend moves out, you're still fine.  You have your fancy apartment and can afford it.   The bigger problem comes if you can't afford the apartment without both the girlfriend and friend contributing.  If so, you should probably avoid this situation.  It's fragile.  Any person leaving would put you in a financially untenable position.  You can look for a new tenant to replace your friend, but you can't exactly rely on getting a new move-in girlfriend on demand.   Neither the girlfriend nor the friend can afford to be on the main lease.  In case of emergency or tragedy, they couldn't replace you as a tenant.  That's why they should sublet.  Then their obligation is to you, not to the landlord.   How much apartment would the girlfriend and friend get if you weren't involved?  What rents would they pay?  That's probably how much rent they should pay for this apartment.  You want a better apartment (or a better location)?  That's on you.   You should only do this if you want to do it.  If you want to share apartments with the girlfriend and friend, then do so.  Work out something equitable.  If you plan on moving in together to reduce your costs, then you don't sound like you are compatible.  Obviously there are reasons to move in with the girlfriend aside from costs.  Why can't the friend get his or her own place?  The added rent probably won't do more than pay for the added room (you could get a one bedroom without the friend).   That points to an alternative way of calculating the friend's contribution:  the difference between a two bedroom and a one bedroom apartment.  That's the additional cost of the bigger apartment.  If the friend can't afford that, then this might not be a good idea.   Make sure that you can afford the apartment if one or both of the friend and girlfriend move out.  You can eventually replace the friend as the tenant but don't rely on doing the same with the girlfriend.  Share utilities evenly.  Possibly groceries too.  The friend should pay at least the added cost of the additional bedroom.  Don't expect either to pay more in the new apartment than they would pay without you.  You should be the only one on the main lease; sublet to them. Now I have been trying to figure out how to split the money that we both earn. From what I can see there are several concepts but none of them really seems ideal to me. There is nothing fair or unfair in such arrangements. It is what you both agree. You can try and make this as scientific as possible. But then there is no golden rule.  For example, your girlfriend makes 2200 now and due to child, she is making 1100. The child is both of your responsibility; so you need to compensate half of her salary loss. 550 and she takes the other half. If you hire a nanny to look after you kinds, it would say cost you 500. But your girlfriend is doing that job, so she should get additional 500 from common pot. Plus due to loss of few years in looking after the children, she has a lost opportunity in career growth. i.e. she may indefinitely make less money than she can... So one gets into all kinds of theories and analysis and any arrangements will have some or the other gaps.  So my suggestion, don't get too scientific about it. Just talk it out as to what you both feel how this should be and arrive it. It is something every individual has to agree. It also make sense to have the large assets [or assets that matter], like house, car etc in clear title and who gets what in case you decide to separate. Other should be incidental. "Generally, when you own something - you can give it as a collateral for a secured loan. That's how car loans work and that's how mortgages work. Your ""equity"" in the asset is the current fair value of the asset minus all your obligations secured by it. So if you own a property free and clear, you have 100% of its fair market value as your equity. When you mortgage your property, banks will usually use some percentage loan-to-value to ensure they're not giving you more than your equity now or in a foreseeable future. Depending on the type and length of the loan, the LTV percentage varies between 65% and 95%. Before the market crash in 2008 you could even get more than 100% LTV, but not anymore. For investment the LTV will typically be lower than for primary residence, and the rates higher. I don't want to confuse you with down-payments and deposits as it doesn't matter (unless you're in Australia, apparently). So, as an example, assume you have an apartment you rent out, which you own free and clear. Lets assume its current FMV is $100K. You go to a bank and mortgage the apartment for a loan (get a loan secured by that apartment) at 65% LTV (typical for condos for investment). You got yourself $65K to buy another unit free and clear. You now have 2 apartments with FMV $165K, your equity $100K and your liability $65K. Mortgaging the new unit at the same 65% LTV will yield you another $42K loan - you may buy a third unit with this money. Your equity remains constant when you take the loan and invest it in the new purchase, but the FMV of your assets grows, as does the liability secured by them. But while the mortgage has fixed interest rate (usually, not always), the assets appreciate at different rates. Now, lets be optimistic and assume, for the sake of simplicity of the example, that in 2 years, your $100K condo is worth $200K. Voila, you can take another $65K loan on it. The cycle goes on. That's how your grandfather did it." Also, does anyone know of any books on doing this sort of thing, i.e. renting out half of your home to a tenant and living in the ret? Head down to your local library. Mine has a state guide for renters and another one for landlords. There will likely be a lot of Nolo Press books around there too.  You can also research the property tax on a lot; many counties run an arcGIS server that will tell you who owns a given property, what the assessed value is and the total tax bill, etc. "Get everything in writing. That includes ownership %, money in, money out, who is allowed to use the place, how much they need to pay the other partners, who pays for repairs, whether to provide 'friends and family' discounts, who is allowed to sell, what happens if someone dies, how is the mortgage set up, what to do if one of you becomes delinquent, etc. etc. etc. Money and friends don't mix. And that's mostly because people have different ideas in their head about what 'fair' means. Anything you don't have in writing, if it comes up in a disagreement, could cause a friendship-ending fight. Even if you are able to agree on every term and condition under the sun, there's still a problem - what if 5 years from now, someone decides that a certain clause isn't fair? Imagine one of you needs to move into the condo because your primary residence was pulled out from under you. They crash at the condo because they have no where else to go. You try to demand payment, but they lost their job. The agreement might say ""you must pay the partnership if you use the condo personally, at the standard monthly rate * # of days"". But what is the penalty clause - is everything under penalty of eviction, and forced sale of the condo and distribution of profits? Following through on such a penalty means the friendship would be over. You would feel guilty about doing it, and also about not doing it [at the same time, your other partner loses their job, and can't make 1/3rd of the mortgage payments anymore! They need the rent or the bank will foreclose on their house!] etc etc etc Even things like maintenance - are the 3 of you going to do it yourselves? Labour distributed how? Will anyone get a management fee? What about a referral fee for a new renter? Once you've thought of all possible circumstances and rules, and drafted it in writing, go talk to a lawyer, and maybe an accountant. There will be many things you won't have considered yet, and paying a few grand today will save you money and friends in the future." Equity means having ownership, and I think that's a REALLY bad idea in the scenario that you described.  If you stay together, there's really no upside to either of you in this scheme.  If you break-up then you'll have a terrible mess, especially if the break-up goes badly.  If she's really building equity, you're going to be faced with several hard questions: If this went bad at the end, it might be worse than a divorce in some sense since at least in the divorce you have established law to sort out the issues.  You'll be on your own here without a formal contract. (Marriage being a special case of a contract for our purposes here.) If she wants to share costs (which seems perfectly fair) then agree to rent and a split on utilities.  If you really insist on going down the path that you described, I think that you'll need some sort of contract, which probably involves a lawyer.  Anything short of that could not be considered having equity at all and will be completely unenforceable in the event of a bad break-up. (There is some notion of a verbal contract, but that's very hard to prove and subject to misunderstanding and misremembering.) Aside from all of these potential problems in event of a break-up, you would probably also be violating the terms of your mortgage, if you have one. From the bank's perspective, you are selling the property that is the collateral for that loan, which you're almost surely not allowed to do.