The formula equivalent of EBITDA for personal finance?
This should not be taken to be financial advice or guidance. My opinions are my own and do not represent professional advice or consultation on my part or that my employer. Now that we have that clear... Your idea is a very good one.  I'm not sure about the benefits of a EBITDA for personal financial planning (or for financial analysis, for that matter, but we will that matter to the side). If you have a moderate (>$40,000) income, then taxes should be one the largest, if not the largest chunk of your paycheck out the door.  I personally track my cash flow on a day-by-day basis. That is to say, I break out the actual cash payments (paychecks) that I receive and break them apart into the 14 day increments (paycheck/14). I then take my expenses and do the same. If you organize your expenses into categories, you will receive some meaningful numbers about your daily liquidity (i.e: cash flow before taxes, after taxes, cash flow after house expenses, ect) This serves two purposes. One, you will understand how much you can actually spend on a day-to-day basis. Second, once you realize your flexibility on a day-to-day basis, it is easy to plan and forecast your expenses.
You could create your own spreadsheet of Cash Flows and use the XIRR function in Excel: The formula is: If it's number of years and the interest is per-annum the formula is the same as the normal one.  this should work on most hand-held calculators. This looks correct to me, for simple interest. If you are dealing with compound interest, the formula would be: So, A = 500000(1+0.036/365)^(30), or 501,481.57, or an interest of 1481.57, assuming the 3.6% is the annual nominal interest rate and it is compounded daily. Note that you are ignoring the depreciation and also ignoring the percentage of customers who will forfeit their debt in the 30 - 60 day period. This is a present value calculation, which excel or any financial calculator can handle.  N = 300 (months) %i = 5/12 or .05/12 depending on the program/calculator PMT = $5000 (the monthly payment) FV = 0 (you want to end at zero balance) This calculates a PV (present value of $855,300)  Chad had it right, but used a calculator that didn't offer the PV function, so he guessed and changed numbers til the answer was clear. user379 makes a good point, but why start inflation calculations at 65, and not now? You look like you're in your 30's, so there's 30 years of inflation, and $60K/yr in today's value will need to be closer to $150K/yr, given about 30 years of 3% inflation. The equation is the same one used for mortgage amortization.  You first want to calculate the PV (present value) for a stream of $50K payments over 20 years at a10% rate.  Then that value is the FV (future value) that you want to save for, and you are looking to solve the payment stream needed to create that future value. Good luck achieving the 10% return, and in knowing your mortality down to the exact year. Unless this is a homework assignment, which need not reflect real life.  Edit - as indicated above, the first step is to get that value in 20 years:  The image is the user-friendly entry screen for the PV calculation. It walks you though the need to enter rate as per period, therefore I enter .1/12 as the rate. The payment you desire is $50K/yr, and since it's a payment, it's a negative number. The equation in excel that results is: =PV(0.1/12,240,-50000/12,0) and the sum calculated is $431,769 Next you wish to know the payments to make to arrive at this number:  In this case, you start at zero PV with a known FV calculated above, and known rate. This solves for the payment needed to get this number, $568.59 The excel equation is: =PMT(0.1/12,240,0,431769) Most people have access to excel or a public domain spreadsheet application (e.g. Openoffice). If you are often needing to perform such calculations, a business finance calculator is recommended. TI used to make a model BA-35 finance calculator, no longer in production, still on eBay, used.  One more update- these equations whether in excel or a calculator are geared toward per period interest, i.e. when you state 10%, they assume a monthly 10/12%. With that said, you required a 20 year deposit period and 20 year withdrawal period. We know you wish to take out $4166.67 per month. The equation to calculate deposit required becomes - 4166.67/(1.00833333)^240= 568.59  HA! Exact same answer, far less work. To be clear, this works only because you required 240 deposits to produce 240 withdrawals in the future. "I've just started using Personal Capital (www.personalcapital.com) after seeing the recommendation at several places.  I believe it gives you what you want to see, but I don't think you can back populate it with old information.   So if you log in and link accounts today, you'll have it going forward. I only put in my investment accounts as I use another tool to track my day-to-day spending.   I use Personal Capital to track my investment returns over time.  How did my portfolio compare to S&P 500, etc.   And here is a shot of the ""You Index"" which I think is close to what you are looking for:" But how do I bring the initial deposit into the equation? Basically, you can't.  Unless you combine two different formulas from Math of Finance into a single expression. The single initial deposit of $1000 will compound for 20 years at 5% compounded annually. The final amount for this part of the deposit will be: V1 = 1000 x (1.05)^20 In addition the series of 20 payments will be an ordinary annuity with a regular payment of $100, with the value on the occasion of the 20th payment given by:  So the final total amount in the account at the end of 20 years will be the sum of these two values... "Note that mutual funds' quarterly/annual reports usually have this number. I generally just let my home-accounting software project my future net worth; its numbers agree well enough with those I've gotten from more ""professional"" sources such as monte-carlo modelling. (They'd agree better if I fed in all the details of my paycheck, but I don't feel like doing the work to keep that up to date.) I'm using Quicken, but I assume MS Money and other competitors have the same capability if you buy the appropriate version." "I think this question is perfectly on topic, and probably has been asked and answered many times.  However, I cannot help myself. Here are some basics however: Personal Finance is not only about math.  As a guy who ""took vector calculus just for fun"", I have learned that superior math skills do not translate into superior net worth.  Personal finance is about 50% behavior.  Take a look at the housing crisis, car loans, or payday lenders and you will understand that the desire to be accepted by others often trumps the math surrounding a transaction. Outline your goals  What is it that you want in life?  A pile of money or to retire early?  What does your business look like?  How much cash will you need?  Do you want to own a ton of rental properties?  How does all this happen (set intermediate goals). Then get on a budget  A budget is a plan to spend your money in advance.  Stick to it.  From there you can see how much money you have to implement various goals.  Are your goals to aggressive?   This is really important as people have a tendency to spend more money then they have.  Often times when people receive a bonus at work, they spend that one bonus on two or three times over.  A budget will prevent this from happening. Get an Emergency Fund  Without an emergency fund, you be subject to the financial whims of people involved in your own life and that of the broader marketplace.  Once you have one, you are free to invest with impunity and have less stress in a world that deals out plenty.  Bad things will happen to you financially, protect against them. The best first investments are simple:  Invest in yourself.  Find a way to make a very healthy income with upward mobility.  Also get out and stay out of debt.  These things are not sexy, but they pay off in the long run. The next best investment is also simple:  Index funds.  These become the bench mark for all other investments.  If you do not stand a good chance of beating the S&P 500 index fund, why bother?  Just dump the money in the fund and sleep well at night." E&amp;P can be valid throug Net Present Value methods, on a field-by-field basis. As no field is ever-lasting, and there Are not an unlimited number of fields, perpetuity-formulaes Are shitty.  FCFF on a per-field basis with WC and Capex, with a definite lifetime.  Thank you for the compliment. Perhaps there is no single formula that accounts for all the time intervals, but there is a method to get formulas for each compound interest period. You deposit money monthly but there is interest applied weekly. Let's assume the month has 4 weeks.  So you added x in the end of the first month, when the new month starts, you have x money in your account. After one week, you have x + bx money. After the second week, you have x + b(x + bx) and so on. Always taking the previous ammount of money and multiplying it by the interest (b) you have. This gives you for the end of the second month:  This looks complicated, but it's easy for computers. Call it f(0), that is: It is a function that gives you the ammount of money you would obtain by the end of the second month. Do you see that the future money inputs are given with relation to the previous ones? Then we can do the following, for n>1 (notice the x is the end of the formula, it's the deposit of money in the end of the month, I'm assuming it'll pass through the compound interest only in the first week of the next month):  And then write:  There is something in mathematics called recurrence relation in which we can use these two formulas to produce a simplified one for arbitrary b and n. Doing it by hand would be a bit complicated, but fortunately CASes are able to do it easily. I used Wolfram Mathematica commands: And it gave me the following formula:  All the work you actually have to do is to figure out what will be f(0) and then write the f(n) for n>0 in terms of f(n-1). Notice that I used the command FullSimplify in my code, Mathematica comes with algorithms for simplyfing formulas so if it didn't find something simpler, you probably won't find it by yourself! If the code looks ugly, it's because of Mathematica clipboard formatting, in the software, it looks like this:  Notice that I wrote the entire formula for f(0), but as it's also a recurrence relation, it can be written as:  That is: f(0)=g(4). This should give you much simpler formulas to apply in this method. I've found the systems that seem to work. Firstly, you need to find how much money is required to pay for the withdrawals after retirement, while still accruing interest.  I couldn't seem to do this with an equation, but this bit of javascript worked: yearsToLast: Number of years of yearly withdrawals yearlyWithdrawal: Amount to withdraw each year interest: Decimal form of yearly compounding interest Now that we have how much is required at the beginning of the retirement, to figure out how much to add yearly to hit this mark, you'd use: amount: Previously found required amount to reach interest: Decimal form of yearly compounding interest yearsSaving: Number of years saving till amount needs to be hit I hope this helps some other poor soul, because I could find squat on how to do this. Max I know this is an old question, but for others who may be wondering the same thing, Kualto.com does precisely this. You enter your expected expenses/income and it shows you the beginning and ending balance of each week. You can navigate ahead as much as you want to see how expenses today will affect your account balance in the future. "The formula is actually as follows: (0.06571441 * V^2) + 15 * V, where V is the value divided by 1,000 which gives us AU$ 23,929 You find the same value using the calculator you linked to if you select ""Investment"" instead of ""Primary Residence"" or uncheck ""I am a first home buyer""  Edit: I don't know how they determine the $AU 821, it might be worth calling them. From looking up the First Home Owner Discount, it looks like no stamp duty may be due if you qualify for the discount: From 1 September 2016, the Northern Territory Government introduced increased stamp duty assistance for first home buyers who purchase an established home in the Northern Territory up to the value of $650 000. The First Home Owner Discount (FHOD) is a full stamp duty concession on the initial $500 000 value of the home, which equates to stamp duty savings of up to $23 928.60. For established homes valued at more than $650 000, a stamp duty saving of $10 000 is available until 31 December 2016. source: Department of Treasury and Finance" "For a personal finance forum, this is too complicated for sustained use and you should find a simpler solution. For a mathematical exercise, you are missing information required to do the split fairly.  You have to know who overlaps and when to know how to do the splits.   For an extreme example, take your dates given: Considering 100 days of calculation period,  If Roommate D was the only person present for the last 10 days, they should pay 100% of the grocery bill as they are the only one eating.   From your initial data set, you can't know who should be splitting the tab for any given day. To do this mathematically, you'd need:  But don't forget ""In Theory, Theory works.  In Practice, Practice works."" Good theory would say make a large, complicated spreadsheet as described above.   Good practice would be to split up the costs in a much, much simpler way."