Quarterly Estimated Tax Safe-Harbor Calculator
The IRS underpayment penalty has nothing to do with what you owe at filing — it has everything to do with whether you paid enough by each quarterly due date. This calculator works out the §6654 safe-harbor minimum you need to hit, splits it across the four quarters, and tells you what to send before the next due date.
Tax year 2026 · Last updated May 10, 2026
Recommended payment by April 15
$4,000
Safe-harbor target for the year: $66,000 (the lesser of $72,000 = 90% of this year, and $66,000 = 110% of last year).
⚠ Year-end gap: $16,000. Estimated penalty if you keep current pace: $1,600.
| Q | Due | Target | Paid | Gap |
|---|---|---|---|---|
| Q1 | April 15 | $16,500 | $12,500 | $4,000 |
| Q2 | June 15 | $33,000 | $25,000 | $8,000 |
| Q3 | September 15 | $49,500 | $37,500 | $12,000 |
| Q4 | January 15 (following year) | $66,000 | $50,000 | $16,000 |
- • Prior-year AGI exceeds the high-income threshold ($150,000; $75,000 if MFS), so the prior-year rule is 110% — not the standard 100%.
- • The prior-year rule produces the smaller target, so that is your safe-harbor minimum. This is the most predictable choice when income is rising.
How it works
- Estimate this year’s total federal tax. Use last year’s return as a starting point, then adjust for known changes (RSU vests, ISO exercises, big bonuses, side income).
- Pull last year’s numbers. You need prior-year total federal tax (Form 1040 line 24) and prior-year AGI (line 11). Prior-year AGI determines whether the 100% or 110% rule applies.
- Add expected withholding and any estimated payments already made. Total federal withholding for the full year (W-2 + 1099) and the dollar sum of estimated payments you’ve already sent.
- Pick the next quarter and read the recommended payment. The calculator shows the lower of the two safe-harbor amounts, the per-quarter target, and exactly what to send for the next due date.
Frequently asked questions
What is the §6654 safe harbor?
IRC §6654 imposes a penalty if you under-pay your federal tax during the year. To avoid the penalty, you must have paid (through withholding + estimates) at least the LESSER of (a) 90% of this year’s tax or (b) 100% of last year’s tax — 110% if your prior-year AGI was over $150,000 ($75,000 if MFS). See IRS Publication 505 (Tax Withholding and Estimated Tax), chapter 2.
When are estimated payments due?
Federal due dates are April 15, June 15, September 15, and January 15 of the following year. If a due date falls on a weekend or federal holiday, it shifts to the next business day. State estimated-tax dates often differ — check your state’s revenue department.
How is withholding treated vs. estimated payments?
Per Treas. Reg. §1.6654-2(d), federal withholding is treated as paid evenly throughout the year — even if it was actually all withheld in December. Estimated payments are credited to the quarter in which they were paid. This is why a Q4 RSU vest can leave you exposed for Q1–Q3 even if you pay in full at year end.
Why is there a $1,000 floor?
IRC §6654(e)(1) says no underpayment penalty applies if your total tax owed at filing is less than $1,000 after subtracting withholding. So if your numbers are small enough, you don’t need to worry about quarterlies at all.
What is the annualized-income method?
If your income is uneven across the year (common for RSU vests, freelance contracts, or commission-heavy sales), Form 2210 Schedule AI lets you "annualize" income by quarter so you don’t get penalized for under-paying in early quarters when you hadn’t earned the income yet. This calculator does NOT model Schedule AI in v1 — it uses the simpler "even payments" assumption.
How is the penalty calculated?
The IRS underpayment-penalty rate is the federal short-term rate + 3 percentage points, reset quarterly (IRC §6621). For 2025–2026 it has hovered around 8% annualized. Form 2210 computes the penalty per-quarter based on how long each shortfall stayed unpaid. The number we show is a planning estimate using a flat 8%, NOT the exact Form 2210 result.
Should I use 90% of this year or 100/110% of last year?
Pick whichever produces the SMALLER target — that’s your minimum. Most people in a stable income year find prior-year-rule simpler because it’s a known number. People expecting big income drops use the 90%-of-current rule. Switching mid-year is fine — the IRS just looks at year-end totals.
Is this tax advice?
No — it’s an estimate based on IRS Publication 505, IRC §6654, and the inputs you provide. It does not consider state estimated tax, AMT, multi-state residency, or annualized-income (Form 2210 Schedule AI) special rules. For decisions involving real money, talk to a licensed tax professional.