THE QUESTION
Why the percentage everyone asks for does not exist
Ask how much to set aside for taxes on 1099 income and the answers come back as percentages: a quarter, a third, somewhere between the two. Each one is a stranger's return rounded to a number. Federal income tax is charged in brackets that depend on taxable income and filing status. Self-employment tax is charged at a flat rate, on a different base. A single percentage folds those two calculations into one figure, and it is accurate only for the person who worked it out.
Two freelancers who invoice the same gross can end the year owing very different amounts. One files jointly with a spouse who has withholding from a salaried job; the other files single with no other income. One drove thousands of business miles and rents a studio; the other worked from a kitchen table and drove nowhere. One lives in a state that charges income tax and one does not. Nothing in the invoices tells them apart. Everything in the returns does.
Which is why the question reads better backwards. The figures that decide the bill — payments received, deductible costs, miles driven — are being generated all year, one at a time. Held as a running total, they produce an estimate that gets closer to the truth every month. Held in memory, they produce a percentage picked in January that nobody revisits until April.
A rule of thumb is somebody else's tax return, rounded off.
THE DATES
The four 2026 estimated tax deadlines
The IRS publishes the estimated tax calendar ahead of the year it covers, and each deadline is tied to a stated stretch of income rather than to a share of the total. That pairing is the part most often missed: the date is only half of the instruction, and the period behind it is the other half.
The periods are not equal quarters. The second covers two months and the fourth covers four, so an earner who divides an annual estimate into four identical instalments is paying against windows of different lengths. A quarter that looked comfortable in June can look wrong in January for no other reason than that.
Form 1040-ES describes the safe-harbour amount as spread across those four payment periods rather than settled in one movement at the end of the year. The instalment structure is part of the instruction and not an administrative detail attached to it, which is the mechanical reason the calendar matters as much as the total does.
- 15 April 2026 — for income received between 1 January and 31 March 2026.
- 15 June 2026 — for income received between 1 April and 31 May 2026, a two-month period.
- 15 September 2026 — for income received between 1 June and 31 August 2026.
- 15 January 2027 — for income received between 1 September and 31 December 2026, a four-month period.
THE PUBLISHED RULES
What Form 1040-ES and the SE calculation describe
Form 1040-ES describes a safe harbour for estimated payments: the smaller of 100 per cent of the federal tax shown on the prior year's return — 110 per cent where the prior year's adjusted gross income was above $150,000 — and 90 per cent of the tax for the current year, spread across the four payment periods. The first of those two figures is knowable in January, because it is already printed on a return that has been filed. The second is not knowable until the year has finished, which is why the prior-year number is the one most people can actually compute in advance.
Self-employment tax is a separate charge with a separate base. The Social Security portion is 12.4 per cent up to the wage base, which is $184,500 for 2026, and the Medicare portion is 2.9 per cent with no ceiling. Both are applied to 92.35 per cent of net self-employment earnings rather than to the whole of it. Net earnings means income after deductible business expenses, so every expense recorded moves this figure as well as the income tax figure — the two calculations share an input.
Mileage is the deduction most often reconstructed from memory in the last week of the year. The IRS standard rate for 2026 is 72.5 cents a mile, published in Notice 2026-10, and it is applied per business mile logged rather than to an annual guess at driving. The rate on its own settles nothing; the log is what the rate multiplies.
None of these rules answers the question they get asked to answer. They describe how a figure is arrived at, not what any particular person's figure is. A published rate, a published wage base and a published set of dates are the fixed part of the problem. The variable part is what you earned and what you spent, and that part lives in your own records.
THE RUNNING TOTAL
What a tracker replaces
A tracker is not a shortcut past any of the above. It is the place the inputs live, so that the estimate becomes arithmetic instead of recall. Payments are logged as they arrive. Expenses are logged against the Schedule C categories they will eventually be reported under, which removes a sorting job that otherwise waits until spring. Trips are logged as trips. The quarterly figure then falls out of numbers that were already written down.
The Freelancer Tax and Income Tracker for the 2026 US tax year is built that way: ten tabs and 888 formulas, with a quarterly planner holding the four IRS deadlines and the safe-harbour calculation, and a dashboard showing income, expenses and what has been set aside so far. Every 2026 figure inside the workbook is cited to the document it came from — Rev. Proc. 2025-32, Notice 2026-10, Notice 2025-54 and Form 1040-ES — so a number can be opened up and checked rather than taken on trust.
What it does not do is decide anything. It estimates, from figures you entered, using rates the IRS published, and it shows its workings — which is mostly a courtesy to whoever reads the file next. An accountant handed a workbook where every category is already matched to a line item spends the appointment on the return rather than on the shoebox.
All of that is organisation and description rather than advice: the IRS publishes the rules the file cites, and a CPA or an Enrolled Agent is who advises on a particular return.