Why is tax being paid on my salary multiple times?
Businesses do not pay income tax on money that they pay out as salary to their employees.  Businesses generally only pay income tax on profit. Profit is the money that comes in (revenue) minus the business expenses.  Payroll to the employees is a deductible business expense. "Your wages are an expense to your employer and are therefore 100% tax deductible in the business income.  The company should not be paying tax on that, so your double-tax scenario, as described, isn't really correct. [The phrase ""double taxation"" with respect to US corporations usually comes into play with dividends.  In that case, however, it's the shareholders (owners) that pay double.  The answer to ""why?"" in that case can only be ""because it's the law.""]"
"You should ask your employer to issue an updated payslip showing the correct gross salary, deductions and net salary, and then repay to the employer the difference between the net salary in your old (wrong) pay slip and the new (correct) one. You should also get them to confirm that they have corrected any information they sent HMRC. At the end of the tax year, when you get a P60 showing your salary for the year, make sure that it is consistent with the corrected salary amount, and check that the tax it shows as being deducted is also correct for that gross salary for the year. If you are still employed by them then you could just ask them to withhold the overpayment in your next salary payment, at which point the income tax would sort itself out because PAYE is calculated based on cumulative totals. If the overpayment had happened at the end of the tax year (March) then there'd be some risk of it messing up your tax payments. In some cases it's also possible that withholding from the next salary payment could make a difference to the total national insurance you end up paying - broadly, if you earn below the ""Primary Threshold"" of £8164/year, you might lose out. If you earn close to the ""Upper Earnings Limit"" of £45000/year, you could end up gaining." One point that I don't see covered in the other answers yet: How does this affect the months that have 5 weeks. Do we actually lose two weeks a year? I get paid every two weeks, and pay day is always a Friday.  Some months, I get paid 3 times - which is always great.  If you live within your means, it's like an extra paycheck.  All other months, I get paid two times.  How many months a year do I get paid 3 times? 2.  It will always be two, because there are 12 months.  If you get paid twice a month, that's 24 pay checks, which is 2 shy of 26 pay checks - what we would expect if we were paid every two weeks.  That means those 2 extra pay checks need to fall somewhere, and they will be on the months where your pay day is hit 5 times.  For example, in 2014, there are 4 months with 5 Fridays: Jan May Aug Oct  I got paid the second Friday of January, so I only got 2 checks in January.  I will be paid on the first Friday of May, which means I will get 3 checks in May.  My other triple-check month this year is October, so of course I am only going to be paid twice in August. It is possible that they only do the hold on the first deposit from a given source. It is probably worth asking if they intend to do the hold on every paycheck or just the first one. Generally this gets corrected when you file returns for both States -- one owes you some refund, and younowe some money to the other. Multistate tax returns are their own special kettle of worms, so you might want to consider hiring a pro to straighten this out -- their software has some tools personal packages don't. In Singapore, this is sufficiently common that the Singapore IRS has a page on their website dedicated to informing employers of how to properly pay this under Responsibilites of an Employer.   Specifically, tax paid by employer is taxable income for the employee (as it's really the employee's responsibility), so they must pay tax for that tax.  A tax-on-tax is computed for the tax paid, which also would be owed by the employer if they were paying the full tax rate for the employee. As a clarification, this is not the employer being truly responsible for the employee's income; this is the employer compensating the employee further to offset their taxable income.  This is effectively a fringe benefit, although it may be particularly useful in countries where either tax evasion is common (and thus an employer must compete with employers willing to pay under the table) or where employers are competing with others in nearby countries with lower tax rates.  It is not the same thing as the employer making your income nontaxable, though, and has implications for your tax filing. Significantly, it is likely that if you have additional income beyond income from that employer, it is likely to be taxed at your highest tax rate, as the employer will likely calculate the tax due based on their income being the only income you have in that year. *Edit based on emphasis in question: I'm not from Singapore nor am I a lawyer, but based on my reading of the IRAS website, it looks like you do not have to file if you have no other source of income, because they have a No-Filing Service which takes income information from your employer automatically and generates a tax bill, which presumably would be fully paid in your case.  This only aplies if you have no other sources of income, however; you still have to file if you have other sources of income since your employer would not know about them. If you are eligible for this service, you should get a letter informing you as such.  They also have a tool to check your filing status on their website. "What theyre fishing for is whether the money was earned in the U.S.  It's essentially an interest shelter, and/or avoiding double taxation.   They're saying if you keep income you make outside the US in a bank inside the US, the US thanks you for storing your foreign money here and doesn't tax the interest (but the nation where you earned that income might).   There is no question that the AirBNB income is ""connected with a US trade or business"".   So your next question is whether the fraction of interest earned from that income can be broken out, or whether IRS requires you to declare all the interest from that account.   Honestly given the amount of tax at stake, it may not be worth your time researching.   Now since you seem to be a resident nonresident alien, it seems apparent that whatever economic value you are creating to earn your salary, is being performed in the United States. If this is for an American company and wages paid in USD, no question, that's a US trade or business. But what if it's for a Swedish company running on Swedish servers, serving Swedes and paid in Kroner to a Swedish bank which you then transfer to your US bank? Does it matter if your boots are on sovereign US soil?  This is a complex question, and some countries (UK) say ""if your boots are in our nation, it is trade/income in our nation""... Others (CA) do not.  This is probably a separate question to search or ask. To be clear, the fact that your days as a teacher or trainee do not count toward residency, is a separate question from whether your salary as same counts as US income." Aside from the fact that probably nobody is ever going to come and ask for that proof unless your amounts get five digits (or you're unlucky), if you never before reimbursed yourself, your old tax declarations would clearly show that. You can't prove a negative, so the only potential is that you had reimbursements before, and an audit might ask you to prove that the new ones are not duplicates of those. In this case, if you have other receipts / proof for all those other reimbursements, they are obviously not duplicates. Because lobbying.  Otherwise such tax optimization schemes would be counteracted with laws after their discovery by our law-making entities... who can be ~~paid~~ lobbied.  Personally I believe if your company uses a country's infrastructure to sell goods for a profit, then you should pay a fair share of that profit to support that infrastructure you use. If you don't want to pay, just don't do business there. But lobbying can alter that logic. I suggest taking a look at your pay stub or pay statement. Your employer should provide you with one for each time you get paid. This shows your gross income (pay period and year to date or YTD for short) and all stuff that gets deducted and how your actual payment is calculated. In my case there are nine things that get taken off: Other things that might show up there are various life or accident insurances, Child Care flexible spending account, legal & pet insurances, long term disability, etc. Some of those are under your control (through benefit election or contribution choices), others you just have to live with. Still, it's worth spending the time to look at it occasionally. "As you clarified in the comments, it is not a contract work but rather an additional temporary assignment with the same employer. You were paid for it in form of a ""bonus"" - one time irregular payment, instead of regular periodic payments. Irregular wage payments fall under the flat rate withholding rule (the 25% for Federal, some States have similar rules for State withholding). This is not taxes, this is withholding. Withholding is money the employer takes from your salary and forwards to the IRS on the account of your tax liability, but it is not in itself your tax liability. When you do your annual tax return, you'll calculate the actual tax you were supposed to pay, and the difference between what was withheld and your actual tax will be refunded to you (or owed by you, if not enough was withheld). You can control the regular pay withholding using W4 form." "When you say ""set aside,"" you mean you saved to pay the tax due in April? That's underpaying. It's a rare exception the IRS makes for this penalty, hopefully it wasn't too large, and you now know how much to withhold through payroll deductions.  Problem is, this wasn't unusual, it was an oversight. You have no legitimate grounds to dispute. Sorry." "Two comments on your calculations: I worked for many years at a community college (Ontario, Canada) where I received an annual salary for the contract period Sept 1, Year N, to August 31, Year (N + 1). For most of that time, the system was 26 pay-cheques a year, one every 14 days. Payroll made most mandatory deductions (union dues, pension, etc.) on a monthly basis, assigning them to one or the other of the two cheques each month.  So there was a fairly large variation in the net amount received in the two cheques.  Plus there were those two ""extra"" cheques each year with very few deductions. (as in the answer of @Kate Gregory) Additionally, Payroll was smart enough to make the last cheque of the contract year for a slightly odd amount, just the correct amount to bring the total gross amount paid to the actual contractual salary, evening out any extra days or rounding error. They would restart the payment schedule anew on the second Thursday in September." "It seems that you think you are freelancing, and they think you are an employee. What's bad for you, the tax office will also think you are an employee if they withhold tax for you. Alternatively, they think you are stupid, and they keep the money, but are actually not paying it to the tax office at all, in which case you will have a bad surprise when you do your tax returns.  First, I'd ask them for proof that they are indeed paying these taxes into some account related to you. I'd then ask a tax adviser for some serious advice. If they are acting out of incompetence and not out of malice, then you should be mostly fine, but your work there will count as employment.  Heaven knows why they treat you as an employee. Check your contract with them; whether it is between you and them or your company and them. It maybe that they never hired a contractor and believe that they have to pay employment tax. They don't. If your company sends them a bill, then they need to pay that bill, 100% of it, and that's it. Taxes are fully your business and your responsibility. As ""quid"" said, if they say they are withholding tax, then at the very least there must be a paystub that proves they have actually been paying these taxes. If they withhold taxes, and there is no paystub, then this looks like a criminal attempt to cheat you.  If they have actually paid taxes properly into your account, then they are merely creating a mess that can hopefully be fixed. But it is probably complicated enough that you need a tax advisor, even if you had none before, since instead of paying to your company, they paid some money to the company, and some to you personally." The vast majority of individual taxpayers in the United States operate on a cash basis of accounting. This means that the assignment of deductions or income to tax year is based on the date of the paycheck.  So the money in that early January 2016 paycheck has been correctly assigned to the 2016 tax year. This is unfortunate for you because you will receive a W-2 for 2016 showing that you had a retirement account. Knowing exactly how many paychecks there are in a year can be very import to know when trying the reach or avoid some thresholds. Even quitting the previous pay period might not have helped. I have seen some companies payout unused vacation, sick and severance over several paychecks. They didn't give you it all in one lump sum, they did it 80 hours a paycheck until the balance owed to the employee was zero. "In the Netherlands its cheaper in some cases to have a mortgage then to own a house.   Example: If you own a house you pay more taxes (because you own something expensive you have to pay ""eigendoms belasting"" < owners tax). So if you instead of owning the house,  keep the mortgage low and only pay the mortgage interest, the interest will be much lower then the tax you would have to pay. The sweet spot (for lowest interest and not having to pay the owners tax) is different for any mortgage but by grandparents use this method and they pay a really small amount for a rather large house."