FICA was not withheld from my paycheck
Should I have a W-2 re-issued? A W-2 can be corrected and a new copy will be filed with the IRS if your employer incorrectly reported your income and withholding on a W-2 that they issued. In this case, though the employer didn't withhold those taxes, they should not reissue the W-2 unless they plan to pay your portion of the payroll taxes that were not withheld. (If they paid your share of the taxes, that would increase your gross income.) Who pays for the FICA I should have paid last year? Both you and your employer owe 7.65% each for FICA taxes. By law your employer is required to pay their half and you are required to pay your half. Both you and your employer owe additional taxes because of this mistake. Your other questions assume that your employer will pay your portion of the taxes withheld. You employer could decide to do that, but this also assumes that it was your employer's fault that the mistakes were made. If you transitioned to resident alien but did not inform your employer, how is that your employer's fault? According to this section in Publication 15:  Collecting underwithheld taxes from employees.   If you withheld no   income, social security, or Medicare taxes or less than the correct   amount from an employee's wages, you can make it up from later pay to   that employee. But you’re the one who owes the underpayment.   Reimbursement is a matter for settlement between you and the employee.   [...] it seems that if the employer withheld less than the correct amount of FICA taxes from you, it is still the employer who owes your FICA taxes to the government, not you. I do not believe there is a way for you, an employee (not self-employed), to directly pay FICA taxes to the government without going through the employer. The employer can deduct the underwithheld amount from you future paychecks (assuming you still work for them), or settle it with you in some other way. In other words, you owe the employer, and the employer owes the government, but you do not directly owe the government. If they do deduct it from your future pay, then they can issue a corrected W-2, to reflect the amount deducted from you. But they cannot issue a corrected W-2 that says FICA were deducted from you if it wasn't.
401(k) withdrawals - early or otherwise - are not subject to FICA or Medicare taxes.  That's because they already were taxed when they were contributed.  (And of course, the earnings from the 401(k) contributions are not earned income and thus are not subject to payroll taxes for that reason.) While 401(k) contributions are exempt from federal (and generally state) income taxes, they aren't exempt from payroll taxes - and as such, you'll see two separate amounts on your W2 and paystub if you contributed: the amount that is subject to those taxes, and the amount that is subject to income tax. So, no, you don't have to pay payroll (FICA, Social Security) taxes on your early withdrawal.  As for the penalty, that is basically an extra tax - so if you withdraw $1000, you pay income tax at your marginal rate plus 10% penalty; if your marginal rate is 25% [and you're not moving across a rate step boundary], you will pay 25%*(1000) + 10%*(1000). "I've been in a similar situation before. While contracting, sometimes the recruiting agency would allow me to choose between being a W2 employee or invoicing them via Corp-2-Corp. I already had a company set up (S-Corp) but the considerations are similar. Typically the C2C rate was higher than the W2 rate, to account for the extra 7.65% FICA taxes and insurance. But there were a few times where the rate offered was identical, and I still choose C2C because it enabled me to deduct many of my business expenses that I wouldn't have otherwise been able to deduct. In my case the deductions turned out to be greater than the FICA savings. Your case is slightly different than mine though in that I already had the company set up so my company related costs were ""sunk"" as far as my decision was concerned. For you though, the yearly costs associated with running the business must be factored in. For example, suppose the following: Due to these expenses you need to make up $3413 in tax deductions due to the LLC. If your effective tax rate on the extra income is 30%, then your break even point is approximately $8K in deductions (.3*(x+3413)=3413 => x = $7963) So with those made up numbers, if you have at least $8K in legitimate additional business expenses then it would make sense to form an LLC. Otherwise you'd be better off as a W2. Other considerations:" You're partially correct, at least in my understanding of this. Yes, the tax credit can be carried forward to future years, but since it is non-refundable it will reduce your tax liability solely. Depending on your tax situation this may result in a bigger refund or it may not. In an example, If you've had $3K withheld from your paycheck toward your income tax and this is also an accurate reflection if your tax liability then taking the NRTC would reduce your tax liability enabling you to be eligible for a refund (due to having already pre-paid more tax than you're liable for). Unfortunately, the tax system in the U.S. is probably more complicated than it looks to you right now. First, you need to understand that there will be taxes withheld from your paycheck, but the amount that they withhold is simply a guess.  You might pay too much or too little tax during the year.  After the year is over, you'll send in a tax return form that calculates the correct tax amount.  If you have paid too little over the year, you'll have to send in the rest, but if you've paid too much, you'll get a refund.  There are complicated formulas on how much tax the employer withholds from your paycheck, but in general, if you don't have extra income elsewhere that you need to pay tax on, you'll probably be close to breaking even at tax time. When you get your paycheck, the first thing that will be taken off is FICA, also called Social Security, Medicare, or the Payroll tax.  This is a fixed 7.65% that is taken off the gross salary.  It is not refundable and is not affected by any allowances or deductions, and does not come in to play at all on your tax return form. There are optional employee benefits that you might need to pay a portion of if you are going to take advantage of them, such as health insurance or retirement savings.  Some of these deductions are paid with before-tax money, and some are paid with after tax money. The employer will calculate how much money they are supposed to withhold for federal and state taxes (yes, California has an income tax), and the rest is yours. At tax time, the employer will give you a form W-2, which shows you the amount of your gross income after all the before-tax deductions are taken out (which is what you use to calculate your tax).  The form also shows you how much tax you have paid during the year. Form 1040 is the tax return that you use to calculate your correct tax for the year.  You start with the gross income amount from the W-2, and the first thing you do is add in any income that you didn't get a W-2 for (such as interest or investment income) and subtract any deductions that you might have that are not taxable, but were not paid through your paycheck (such as moving expenses, student loan interest, tuition, etc.)  The result is called your adjusted gross income. Next, you take off the deductions not covered in the above section (property tax, home mortgage interest, charitable giving, etc.).  You can either take the standard deduction ($6,300 if you are single), or if you have more deductions in this category than that, you can itemize your deductions and declare the correct amount. After that, you subtract more for exemptions.  You can claim yourself as an exemption unless you are considered a dependent of someone else and they are claiming you as a dependent.  If you claim yourself, you take off another $4,000 from your income. What you are left with is your taxable income for the year.  This is the amount you would use to calculate your tax based on the bracket table you found. California has an income tax, and just like the federal tax, some state taxes will be deducted from your paycheck, and you'll need to fill out a state tax return form after the year is over to calculate the correct state tax and either request a refund or pay the remainder of the tax.  I don't have any experience with the California income tax, but there are details on the rates on this page from the State of California. Well as it was stated by others it isn't taken out of their paychecks, it's paid for by the employer, however these same individuals are exempt from paying into social security over a certain limit so if they are able to pocket that money up front why do they need to collect government benefits when they have extra income the rest of us do not have from not having to pay into social security. "Following up on this, here is what I did. First, I called my benefits provider.  They had documentation of my election over the phone, which then allowed them to retroactively fix the problem. Had they not had this documentation, I would have been out of luck. Second, the next step for ""fixing"" occurred when I received my W-2 for this position. This W-2 mistakenly showed the amount for my medical FSA in box-10 of my W-2 as the same dependent care FSA. This requires calling/emailing my benefits and payroll department to get an updated W-2..." Welcome to the real world. BTW, you have far too rosy a view of this if you think you're only paying 28.5% of your income in taxes. Remember that your employer theoretically pays half your FICA tax. But as far as they're concerned, that's part of the cost of having you as an employee. If FICA was abolished, supply and demand would quickly push salaries up by an amount equal to the FICA tax. So add another 7.65% to your taxes. Plus your employer has to pay unemployment tax (federal unemployment tax is $420 per employee per year, states vary) and workman's compensation tax (no idea how much that is) for the privilege of having you as an employee. You likely pay sales taxes on most everything you buy. I believe sales tax in Massachusetts is 6.25%. Assuming you pay that on only half of what you buy, add another 3% or so. Do you work for a corporation? Between when they sell the fruits of your labor and when they pay you, they have to pay corporate income tax. There are a lot of deductions so that gets complicated, but figure another few percent. Do you drive a car? You're paying gas tax -- 41.9 cents per gallon in MA. Do you smoke or drink alcohol? Extra taxes on those. Travel by plane or stay in a hotel? More special taxes. When you get around to buying a house, you'll pay property taxes on it every year, year after year. For me in Michigan that's another 3% of my income. I understand it's a lot more in Massachusetts. Etc, many other smaller taxes that add up. It is true that with a job that pays you via payroll check that will result in a W-2 because you are an employee, the threshold that you are worried about before you have to file is in the thousands. Unless of course you make a lot of money from bank interest or you have income tax withheld and you want it refunded to you. Table 2 and table 3 in IRS pub 501, does a great job of telling you when you must.  For you table 3 is most likely to apply because you weren't an employee and you will not be getting a W-2. If any of the five conditions listed below applied to you for 2016, you must file a return. You owe any special taxes, including any of the following. a. Alternative minimum tax. (See Form 6251.)    b. Additional tax on a   qualified plan, including an individual retirement arrangement (IRA),   or other tax­favored account.  (See Pub. 590­A, Contributions to   Individual Retirement Arrangements (IRAs); Pub. 590­B, Distributions   from  Individual Retirement Arrangements (IRAs); and Pub. 969, Health   Savings Accounts and Other Tax­Favored Health  Plans.) But if you are   filing a return only because you owe this tax, you can file Form 5329   by itself.   c. Social security or Medicare tax on tips you didn't   report to your employer (see Pub. 531, Reporting Tip Income) or on    wages you received from an employer who didn't withhold these taxes   (see Form 8919).    d. Write­in taxes, including uncollected social   security, Medicare, or railroad retirement tax on tips you reported to   your  employer or on group­term life insurance and additional taxes on   health savings accounts. (See Pub. 531, Pub. 969,  and the Form 1040   instructions for line 62.)   e. Household employment taxes. But if you   are filing a return only because you owe these taxes, you can file    Schedule H (Form 1040) by itself. f. Recapture taxes. (See the Form   1040 instructions for lines 44, 60b, and 62.) You (or your spouse if filing jointly) received Archer MSA, Medicare Advantage MSA, or health savings account  distributions. You had net earnings from self­employment of at least $400. (See Schedule SE (Form 1040) and its instructions.) You had wages of $108.28 or more from a church or qualified church­controlled organization that is exempt from employer  social   security and Medicare taxes. (See Schedule SE (Form 1040) and its   instructions.) Advance payments of the premium tax credit were made for you, your spouse, or a dependent who enrolled in coverage  through the Health   Insurance Marketplace. You should have received Form(s) 1095­A showing   the amount of the advance  payments, if any. It appears that item 3: You had net earnings from self­employment of at least $400. (See Schedule SE (Form 1040) and its instructions.) would most likely apply. It obviously is not too late to file for 2016, because taxes aren't due for another month. As to previous years that would depend if you made money those years, and how much.