"How to Calculate Quarterly Estimated Taxes"

How much should a quarterly estimated payment actually be? Ask ten freelancers and you will get ten guesses, several of them a flat "25% of whatever I made." A guess is how penalties happen. There are exactly two correct ways to size estimated payments — one based on this year's projected tax, one based on last year's actual tax — and the second is so close to foolproof that it is the one to learn first. This walkthrough does both, in order, with the 2026 numbers, using the Estimated Tax Payment Calculator. For the deadlines and the why, pair it with estimated tax payments: when and how.

Who this is for

If income arrives without federal tax withheld — self-employment, freelance, investment, rental, large capital gains — the IRS still wants the tax during the year, in four installments, not in one lump at filing. Generally you must pay estimates if you expect to owe $1,000 or more after withholding and credits. Employees with only W-2 wages usually do not need to; their withholding handles it.

Method A — The safe harbor (use this one)

The safe harbor is a rule that says: pay in enough relative to last year's tax and no underpayment penalty applies, regardless of how this year turns out. That last clause is why it is powerful — it works even in a year your income explodes, because it is anchored to a number that is already known and final.

The required total for the year is the smaller of:

• 90% of the current year's total tax, or
• 100% of last year's total tax — 110% if last year's adjusted gross income was over $150,000.

Pick the prior-year figure and you are sizing payments off a fact, not a forecast. Divide that total by four; that is each quarterly payment.

Worked example. Last year's total tax was $14,000, prior-year AGI under $150,000:

Pay $3,500 each quarter and no underpayment penalty applies even if this year's income — and this year's actual tax — comes in far higher. You would still owe the extra real tax at filing, but penalty-free. That is the trade the safe harbor offers: certainty now, settle the remainder in April.

Method B — The current-year projection (more accurate, more work)

The safe harbor protects you from penalties; it does not guarantee you are paying the right amount this year. If income dropped, prior-year safe harbor overpays. If you want each payment to track reality, project the current year:

1. Estimate annual net self-employment profit and any other untaxed income.
2. Compute self-employment tax with the Self-Employment Tax Calculator (15.3% of 92.35% of net profit, capped at the 2026 wage base).
3. Compute federal income tax on taxable income with the Federal Income Tax Calculator — and remember to subtract the half-SE-tax deduction first.
4. Add them, subtract expected credits and any withholding, divide by four.

Worked example. Freelancer, $70,000 projected net profit, single, 2026:

The Estimated Tax Payment Calculator runs this stack end to end so you are not chaining tools by hand.

Which method to use

A common, sensible default for an established freelancer: size payments on the prior-year safe harbor for penalty protection, and if this year is clearly bigger, set aside the extra real tax separately so April's true-up is funded.

The deadlines are the other half

Sizing the payment correctly and paying it late still triggers a penalty, because the penalty is calculated per-period. The four 2026 federal due dates fall in April, June, September, and January of the following year — the exact dates are listed in 2026 tax filing deadlines, and the period structure is explained in estimated tax payments: when and how. The note worth internalizing: the four "quarters" are not equal calendar quarters, so do not assume even three-month spacing.

The mixed case: a W-2 job plus side income

Many people are not pure freelancers — they have a W-2 job and untaxed side income. There is a cleaner fix here than four estimated payments, and most people miss it: increase W-2 withholding to cover the side income, using Step 4(c) of the W-4. Withholding is treated as paid evenly across the year regardless of when it actually happened, which means a December withholding bump can retroactively cure an earlier-quarter shortfall in a way a late estimated payment cannot. For someone with a steady paycheck and modest side income, raising withholding is simpler and more forgiving than managing a separate quarterly schedule. Reserve formal estimated payments for when side income is large relative to wages, or when there is no W-2 to adjust. The W-4 lever is detailed in how to adjust your W-4 for maximum take-home pay.

A full-year worked plan

Tie the methods together for the $70,000 freelancer, single, 2026, whose prior-year total tax was $12,000 (AGI under $150,000):

This is the practical synthesis: size payments on the prior-year safe harbor so a penalty is impossible, and reserve the difference between projected and safe-harbor tax in a separate account so April's true-up is funded rather than a shock. Penalty-proof and cash-ready is the goal, not a single perfect number.

What a missed quarter actually costs

The underpayment penalty is effectively interest, charged per period from the date the payment was due until it is paid. It is not catastrophic on a small shortfall, but it is pure waste — there is no deduction for it and no upside. More importantly, an early-quarter miss compounds: the shortfall accrues across every subsequent period until covered, so a Q1 miss discovered in Q4 has been running the whole year. The lesson is not "panic over a small slip" but "the safe harbor exists precisely so this never has to be calculated" — anchor to it and the penalty question disappears.

Quick answers

Can I just pay 25% of my income each quarter?

No. That ignores the standard deduction, the bracket structure, and the SE-tax base, and it has no relationship to the safe harbor. It will be wrong in one direction or the other — usually overpaying low earners and underpaying higher ones.

What if my income is uneven across the year?

Either keep payments level on the prior-year safe harbor (simplest), or use the annualized income method, which sizes each payment to income actually earned by that point — useful for seasonal work. The annualized method is more paperwork; the safe harbor sidesteps the problem entirely.

Do estimated payments cover state tax too?

No. States with income tax run their own estimated-payment systems and deadlines. Check the state income tax guide for all 50 states and your state Department of Revenue.

I underpaid one quarter — can I fix it by overpaying the next?

It helps but does not fully erase it. The penalty is computed per period, so a shortfall in an early quarter accrues until covered. Catching up sooner reduces it; it does not retroactively undo it.

Is the safe harbor 100% or 110%?

100% of last year's total tax, or 110% if last year's AGI exceeded $150,000. Use the higher figure if you are over that threshold.

How we keep this accurate

The 90% / 100% / 110% safe-harbor thresholds, the $1,000 filing trigger, and the period structure follow current IRS rules for estimated tax (Form 1040-ES). The 2026 brackets, the $16,100 standard deduction, the 15.3% SE rate, the 92.35% factor, and the $184,500 Social Security wage base are the projected 2026 figures used across the Estimated Tax Payment Calculator and Self-Employment Tax Calculator, reconciled to the official IRS and Social Security Administration releases at year-end. Every figure here is a planning projection, not a filed certainty; a CPA or Enrolled Agent should confirm the right method and amount for your specific income pattern.