Quarterly Estimated Tax Calculator for Freelancers — Safe Harbor & Q3 2026 Due Sept 15

1. Your numbers

Last year's total tax (2025 Form 1040, line 24)

Not what you owed in April — the total tax for the whole year.

$

Last year's AGI (2025 Form 1040, line 11)

Only used to decide if you need 100% or 110%.

$

Filing status

Already paid toward this year (Q1 + Q2 estimates + any withholding)

Include W-2 withholding from a job or a spouse's job — it counts.

$

Optional: estimate this year instead (if your income dropped)

Expected net self-employment profit this year

Revenue minus business expenses, for the full year.

$

Other taxable income (W-2 wages, spouse, interest)

$

Assumed effective income-tax rate on taxable income

Brackets change yearly, so this one is yours to set — check your last return's total tax ÷ taxable income.

%

Standard/itemized deduction you expect to take

Look up the current-year figure on irs.gov — it is inflation-adjusted every year.

$

Social Security wage base for the year

Also inflation-adjusted annually — confirm on ssa.gov.

$

2. What to do

Estimate only — this is not tax advice, and it does not know about credits, AMT, QBI, state tax, or an irregular income year. Verify every current-year figure on irs.gov before you send money.

Why "safe harbor" is the number that matters

The IRS underpayment penalty is not about guessing this year right. You are protected if your payments for the year hit whichever of these is smaller:

90% of what you end up owing this year, or
100% of last year's total tax — 110% if last year's AGI was over $150,000 ($75,000 if married filing separately).

The second one is the useful one: it is a known number off a return you already filed. Pay it in four even pieces and the penalty cannot touch you, even if you have a blowout year. That is what this calculator solves for.

The 2026 quarterly due dates: April 15, June 15, September 15, and January 15, 2027. Miss one and the penalty accrues per quarter — it is interest, not a flat fine, so paying late-but-soon is much better than waiting for April.

The withholding trick: estimated payments are penalized by when you paid them, but withholding is treated as if it were spread evenly across the whole year. If you are behind and you or your spouse has a W-2 job, raising withholding for the rest of the year can retroactively patch earlier quarters in a way a Q3 estimate cannot.

Freelancer Tax Kit — $19

The calculator gives you the number. The kit is everything around it, so you are not rebuilding this every quarter:

Safe-harbor tracker spreadsheet (Excel + Google Sheets) — enter last year's tax once, it tells you each quarter's amount and what is still outstanding.
Deduction checklist for 1099 work — home office, mileage, health insurance premiums, half of SE tax, retirement, the ones people miss.
Mileage & expense log formatted to survive an audit.
How to actually pay — IRS Direct Pay walkthrough with the exact menu choices (the "reason for payment" screen is where people misfile).
Quarterly reminder calendar (.ics) for all four 2026–2027 dates.

Get the kit — $19

One-time payment, instant access, no subscription. Your access link is shown on the checkout page and on your Stripe receipt.