September estimated taxes (Q3 payment)

Mid-year checkpoint: catch up or trim while staying inside safe harbor. Prep only — we don’t e-file.

By The PiggyMath Editorial Desk Last updated August 11, 2026 ✓ Due dates checked against IRS Form 1040-ES (2026)

Next federal due date

Tax year 2026 · third installment (Q3)

Tuesday, September 15, 2026

Income period: June 1 – August 31, 2026. Full calendar and .ics download: quarterly tax deadlines.

Who must pay this installment?

The IRS expects tax as income is earned. If you expect to owe at least $1,000 when you file — which happens quickly once freelance profit is more than a few thousand dollars — you generally need four Form 1040-ES estimated payments. Employees usually cover this through paycheck withholding; freelancers, contractors, and many side-hustle earners do not.

September is the mid-year correction point: if Q1/Q2 were light or heavy relative to the rest of the year, adjust now while you still have one installment left (January 15, 2027) before filing season.

Safe harbor — stay penalty-safe

Meet either target and you avoid the underpayment penalty even if you owe more at filing:

90% of the tax you will owe for 2026, or
100% of the tax shown on your 2025 return (110% if 2025 AGI was over $150,000)

Size the floor with the safe harbor calculator. If income is lumpy, compare equal installments vs annualisation on the Form 2210 helper.

Worked path (about five minutes)

Project full-year SE + federal (+ state/QBI if you need them) in the freelancer tax estimator.
Turn that into a Q3 payment amount with the quarterly tax calculator.
Confirm you are still on track for safe harbor; refresh your transfer habit with the set-aside calculator.
Pay on the IRS site (below). PiggyMath does not send money or e-file.

Example framing: if your estimator says ~$12,000 total federal tax for the year and you have already paid $6,000 in Q1+Q2, a straightforward equal-installment plan still points to about $3,000 for September (and another ~$3,000 by January 15, 2027) — then check safe harbor so you are not under-paying relative to last year’s return.

How to pay (official IRS)

IRS Direct Pay — bank account, no fee, confirmation number.
IRS payments hub — Online Account, EFTPS, card (fee), or check.
About Form 1040-ES and the current 2026 Form 1040-ES (PDF) if you mail a voucher.

If your state has an income tax, it usually wants its own estimated payment on a similar schedule through its own portal.

Other 2026 seasons

April 15 (Q1) · June 15 (Q2) · September 15 (Q3) · January 15, 2027 (Q4) · seasons hub

Frequently asked questions

When is the September 2026 estimated tax payment due?

Tuesday, September 15, 2026. It is the third federal estimated-tax installment for tax year 2026 and covers income earned June 1 through August 31, 2026.

Who must pay the Q3 estimated tax?

If you expect to owe at least $1,000 in federal tax when you file — common once freelance profit is more than a few thousand dollars — you generally need Form 1040-ES estimated payments. Employees usually cover this through withholding; freelancers and the self-employed usually do not.

How do I avoid an underpayment penalty?

Meet the IRS safe harbor: pay at least 90% of this year’s tax, or 100% of last year’s tax (110% if prior-year AGI was over $150,000). Equal quarterly installments that hit either target keep you penalty-safe even if you owe more at filing.

Does PiggyMath e-file or send money to the IRS?

No. PiggyMath is prep only — estimates and planning helpers that run in your browser. Pay through IRS Direct Pay, your IRS Online Account, EFTPS, or a Form 1040-ES voucher.

Where are all 2026–2027 deadlines?

See the quarterly tax deadlines page for every due date plus a downloadable calendar file.

Sources

Estimates only — not tax, legal, or filing advice. How we check our math →