9 calculators for the figures independent workers most often get wrong, each one built on rates read from irs.gov and each one showing its arithmetic rather than a single answer.
What you owe
Income tax and self-employment tax both fall on 1099 income, and nobody withholds either. This runs them in the order the return does, on your own figures, and shows every step from profit to the total.
Self-employment tax is 15.3% on 92.35% of your profit, and it is charged whether or not you owe a dollar of income tax. This shows the whole calculation, including the half you deduct back.
The penalty is figured separately for each payment period, so the only number worth knowing is what to pay by each date. Last year's tax is the one figure you can know in advance.
What you can deduct
72.5 cents through 30 June and 76 cents from 1 July. Split your log at that date, or the total is wrong in one direction or the other.
Below the threshold everyone gets 20%. Above it, a specified service business gets nothing and everyone else meets a wage limit. This shows which side you are on.
Your contribution reduces the earnings your contribution is a percentage of. Publication 560 resolves the circle with a worksheet rather than arithmetic, and this is that worksheet.
Which way costs less
An employer pays half your Social Security and Medicare. Working for yourself, you pay both halves. This is the gap, and the hourly rate that closes it.
Five dollars a square foot, and never more than 300 of them. The regular method has no cap — and it is the only one that carries the excess forward or claims depreciation.
Both methods need the same log. Only one of them lets you change your mind later — and only if you pick it first.