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When one pays Quarterly Estimated Self Employment Taxes, exactly what are they paying?
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.