Estimated Taxes after surge in income
You will not necessarily incur a penalty.  You can potentially use the Annualized Income Installment method, which allows you to compute the tax due for each quarter based on income actually earned up to that point in the year.  See Publication 505, in particular Worksheet 2-9.  Form 2210 is also relevant as that is the form you will use when actually calculating whether you owe a penalty after the year is over. On my reading of Form 2210, if you had literally zero income during the first quarter, you won't be expected to make an estimated tax payment for that quarter (as long as you properly follow the Annualized Income Installment method for future quarters).  However, you should go through the calculations yourself to see what the situation is with your actual numbers. "Well a definitive answer would require a lot of information.  Instead of posting that kind of info online, you should take a look at the instructions for Form 2210 and in particular ""Schedule AI -- Annualized Income Installment Method,"" which corrects the penalty for highly variable income.   Using this form you will likely be able to avoid the penalty, but it is hard to know for sure."
FICA taxes are separate from federal and state income taxes. As a sole proprietor you owe all of those.  Additionally, there is a difference with FICA when you are employed vs. self employed.  Typically FICA taxes are actually split between the employer and the employee, so you pay half, they pay half. But when you're self employed, you pay both halves. This is what is commonly referred to as the self employment tax. If you are both employed and self employed as I am, your employer pays their portion of FICA on the income you earn there, and you pay both halves on the income you earn in your business. Edit: As @JoeTaxpayer added in his comment, you can specify an extra amount to be withheld from your pay when you fill out your W-4 form. This is separate from the calculation of how much to withhold based on dependents and such; see line 6 on the linked form. This could allow you to avoid making quarterly estimated payments for your self-employment income. I think this is much easier when your side income is predictable. Personally, I find it easier to come up with a percentage I must keep aside from my side income (for me this is about 35%), and then I immediately set that aside when I get paid. I make my quarterly estimated payments out of that money set aside.  My side income can vary quite a bit though; if I could predict it better I would probably do the extra withholding. Yes, you need to pay taxes for FICA and federal income tax.  I can't say exactly how much you should withhold though. If you have predictable deductions and such, it could be lower than you expect. I'm not a tax professional, and when it comes doing business taxes I go to someone who is. You don't have to do that, but I'm not comfortable offering any detailed advice on how you should proceed there. I mentioned what I do personally as an illustration of how I handle withholding, but I can't say that that's what someone else should do. "Your question does not say this explicitly, but I assume that you were once a W-2 employee.  Each paycheck a certain amount was withheld from your check to pay income, social security, and medicare taxes.  Just because you did not receive that amount of money earned does not mean it was immediately sent to the IRS.  While I am not all that savvy on payroll procedures, I recall an article that indicated some companies only send in withheld taxes every quarter, much like you are doing now.  They get a short term interest free loan.  For example taxes withheld by a w-2 employee in the later months of the year may not be provided to the IRS until 15 January of the next year.   You are correct in assuming that if you make 100K as a W-2 you will probably pay less in taxes than someone who is 100K self employed with 5K in expenses.  However there are many factors.  Provided you properly fill out a 1040ES, and pay the correct amount of quarterly payments, you will almost never owe taxes.  In fact my experience has been the forms will probably allow you to receive a refund.  Tax laws can change and one thing the form did not include last year was the .9% Medicare surcharge for high income earners catching some by surprise.    As far as what you pay into is indicative of the games the politicians play.  It all just goes into a big old bucket of money, and more is spent by congress than what is in the bucket.  The notion of a ""social security lockbox"" is pure politics/fantasy as well as the notion of medicare and social security taxes.  The latter were created to make the actual income tax rate more palatable.     I'd recommend getting your taxes done as early as possible come 1 January 2017.  While you may not have all the needed info, you could firm up an estimate by 15 Jan and modify the amount for your last estimated payment.  Complete the taxes when all stuff comes in and even if you owe an amount you have time to save for anything additional.  Keep in mind, between 1 Jan 17 and 15 Apr 17 you will earn and presumably save money to use towards taxes.  You can always ""rob"" from that money to pay any owed tax for 2016 and make it up later. All that is to say you will be golden because you are showing concern and planning.  When you hear horror stories of IRS dealings it is most often that people spent the money that should have been sent to the IRS." If you have non-salary income, you might be required to file 1040ES estimated tax for the next year on a quarterly basis. You can instead pay some or all in advance from your previous year's refund. In theory, you lose the interest you might have made by holding that money for a few months. In practice it might be worth it to avoid needing to send forms and checks every quarter. For instance if you had a $1000 estimated tax requirement and the alternative was to get 1% taxable savings account interest for six months, you'd make about $3 from holding it for the year. I would choose to just pay in advance. If you had a very large estimation, or you could pay off a high-rate debt and get a different effective rate of return, the tradeoff may be different. "Employers withhold at rates specified in Circular E issued by the IR. You can request that  additional money be withheld (not an issue here) or you can have  reduced withholding by claiming additional allowances on a W-4 (i.e.,  more than just for you and spouse and dependents) if you believe that  this will result in withholding that will more closely match the tax due.  (Note added in edit):Page 2 of the W-4 form has worksheets that can be used to figure out how many additional allowances to request. Also, I wonder if your withholding will be 37% or final tax bill be  26% of your adjusted gross income.  The tax brackets are the tax  on marginal income. If you are in the 28% tax bracket, you owe 28 cents in tax for each additional dollar of income, not 28 cents in tax for every dollar of income.  Your overall tax might well be less than 20% of your income.  As a specific example, in 2011 a married taxpayer filing jointly would be in the  (highest) 35% tax bracket if the taxable income was $379,150 or more (marginal tax rate of 35% is applicable to every dollar more than $379,150) but the tax on  $379,150 itself works out to be $102,574 or 27.05% of the taxable income. So if you do expect to be earning around $350K or more in salary between now and December 31 to hit that 26% that you expect you will owe, you might want to consider paying a tax accountant for advice on how to fill out your W-4 form for your new employer rather than relying on an Internet forum such as this for free advice. Note added in edit:  Your comment ""... it is a cocktail of ... federal taxes, state taxes, local taxes, health care ..."" on the earlier version of my answer does raise the question of whether you want your employer to withhold 26% instead of 37% and have the money go to meet all these obligations or just 26% towards your Federal income tax liability only. The Federal W-4 form affects only how much money is withheld from your paycheck and sent to the US Treasury.  Some of the money that each of your employers withholds (Social Security and Medicare taxes) is not affected by what you put down on  the W-4 form.  Now, if you hold two jobs and the total income shown on your W-2s is larger than the SS limit, you will  have had too much Social Security taxes withheld, and the excess will be a credit towards your Federal income tax liability.  You have self-employment income too on which you owe Social Security and Medicare taxes and you are making estimated tax payments. The excess Social Security tax payment can count towards this too (as well as income tax on your Schedule C income).  Thus, if your new employer is withholding too much, you might be able to skip making the fourth quarterly payment of estimated tax or make a reduced payment (there is no requirement that the four installments  must be equal).  In short, there are lots of ramifications that you need to take into account before deciding that 26% is the right number. Instead of filling out a W-4  all by yourself right away, I strongly recommend  reading up a lot on income taxes, or play with a tax preparation program (last year's version will do a pretty good job of at least getting you in the right ballpark), or consult with a tax accountant." Yes, this extra income would be taxed at your marginal rate because it is increasing your total income. This does not necessarily apply to all income, however. Capital gains are taxed at a different rate. Depending on the amount of extra work, you may wish to consider setting up a corporation. Corporations are taxed entirely differently. This would also give you the opportunity to write off far more of your expenses, but be aware of double taxation. Investopedia has a good article on double taxation. The issue is that the corporation must pay taxes on the revenue and then, when you take out the money either as salary or dividends, you personally will pay tax. It may leave you better off, even with the double taxation. Dividends are taxed at a lower rate than your marginal tax rate, generally. And you can write off much more inside a corporation. If considering this, talk to an accountant and discuss your expected revenue from consulting. The accountant should be able to quantify the costs and benefits. In my opinion, I would: If the income is from this year, you can tax shelter $59,000 plus somewhere between $50,000 and $300,000 depending on age, in a 401(k) and defined benefit plan. This will take care of the current tax burden. Afterwards, set aside your remaining tax liability in cash. The after-tax money should be split into cash and the rest into assets. The split depends on your level of risk tolerance. Build a core portfolio using highly liquid and non-correlated ETFs (think SPY, TLT, QQQ, ect.). Once these core positions are locked in. Start lowering your basis by systematically selling a 1 standard deviation call in the ETF per 100 units of underlying. This will reduce your upside, extend your breakeven, and often yield steady income. Similarly, you can sell 1 standard deviation iron condors should the VIX be high enough. Point is, you have the money to deploy a professional-type, systematic strategy that is non-correlated, and income generating. You should simply withdraw the excess contributions by April 15. You have until October 15 if you go through the extra step of filing an amended tax return.  https://investor.vanguard.com/ira/excess-contribution It unnecessary for you to pay the 6% penalty. You should wait until you can estimate your 2016 accurately before making your 2016 contribution. If your income is too high for the Roth IRA, you might instead pursue the backdoor Roth IRA strategy:  https://www.bogleheads.org/wiki/Backdoor_Roth_IRA The answer to this question requires looking at the mathematics of the Qualified Dividends and Capital Gains Worksheet (QDCGW). Start with Taxable Income which is the number that appears on Line 43 of Form 1040.  This is after the Adjusted Gross Income has been reduced by the Standard Deduction or Itemized Deductions as the case may be, as well as the exemptions claimed.   Then, subtract off the Qualified Dividends and the Net Long-Term Capital Gains (reduced by Net Short-Term  Capital Losses, if any) to get the non-cap-gains part of the Taxable Income. Assigning somewhat different meanings to the numbers in the OPs' question, let's say that the Taxable Income is $74K of which $10K is Long-Term Capital Gains leaving $64K as the the non-cap-gains taxable income on Line 7 of the QDCGW.   Since $64K is smaller than $72.5K (not $73.8K as stated by the OP) and this is a MFJ return, $72.5K - $64K = $8.5K of the long-term capital gains are taxed at 0%. The balance $1.5K is taxed at 15% giving $225 as the tax due on that part.   The 64K of non-cap-gains taxable income has a tax of $8711 if I am reading the Tax Tables correctly, and so the total tax due is $8711+225 = $8936.  This is as it should be; the non-gains income of $64K was assessed the tax due on it, $8.5K of the cap gains were taxed at 0%, and $1.5K at 15%. There are more complications to be worked out on the QDCGW for high earners who attract the 20% capital gains rate but those are not relevant here.