Answer
How do I calculate my quarterly estimated tax payments?
Short answer
Two methods, both safe-harbor protected. Method 1 (prior-year safe harbor): take last year's total federal tax (Form 1040 Line 24), multiply by 110% if your prior-year AGI exceeded $150,000, divide by 4. Pay that amount each quarter. Method 2 (current-year 90% safe harbor): project your current-year tax, target 90% of it across the four payments. The prior-year method is lower-effort and lower-risk.
Two methods, both safe-harbor protected
Method 1: prior-year safe harbor
Use last year's tax bill, divided by 4
Last year's total tax (Line 24)
$32,000
Multiplier (110% if AGI > $150K)
×1.00
Annual target
$32,000
÷ 4 quarterly payments
÷ 4
Pay each quarter
$8,000
Best when income is rising. Caps obligation at last year's level regardless of how high current-year income climbs.
Method 2: current-year 90%
Project this year's tax, target 90%
Projected current-year tax
$50,000
Safe harbor multiplier
×0.90
Annual target
$45,000
÷ 4 quarterly payments
÷ 4
Pay each quarter
$11,250
Best when income is falling or you want to avoid lending the IRS money interest-free.
Either method, paid on time across the four deadlines, eliminates the underpayment penalty entirely.
The prior-year method, step by step. Pull last year's Form 1040 and find Line 24 (total tax). If your prior-year AGI was over $150,000, multiply that number by 1.10. Divide the result by 4. That is your quarterly payment, due on April 15, June 15, September 15, and January 15. The IRS guarantees no underpayment penalty regardless of how high your current-year income climbs, as long as you make those four equal payments on time.
A worked example. Last year's total tax was $32,000 and prior-year AGI was $145,000 (under the $150K threshold, so no 110% multiplier). Divide $32,000 by 4 to get $8,000. Pay $8,000 every quarter. Even if current-year income doubles to $300,000 and the actual tax is $50,000, the prior-year safe harbor of $32,000 paid in four installments keeps you penalty-free. You owe the $18,000 difference at filing on April 15 of next year, but no penalty applies.
The current-year method, step by step. Project your annual net profit. Calculate SE tax (net profit times 0.9235 times 0.153, capping the SS portion at the wage base of $176,100 in 2026). Calculate federal income tax on (net profit minus half of SE tax minus standard deduction minus 20% QBI deduction) using current-year brackets. Add SE tax and income tax. Multiply by 0.90. Divide by 4. Pay that amount each quarter, adjusting if income shifts.
When to use which. The prior-year method wins if your income is rising or unpredictable, because it caps your obligation at last year's tax. The current-year method wins if your income is falling or you want to avoid lending the IRS money interest-free for months. The current-year method requires more bookkeeping discipline because you need accurate monthly P&Ls to project reliably.
What to ignore. The IRS Form 1040-ES worksheet that ships with the IRS Estimated Tax for Individuals instructions is the official version of these calculations. It is comprehensive but designed for someone projecting from scratch. If your situation is already running (you filed last year), the prior-year safe harbor is far simpler. If your situation is new (first year of self-employment), use the current-year method with conservative income assumptions.
Which method fits your situation
Pick by income trajectory.
Both methods are equally valid IRS-wise. The difference is which one matches your cashflow situation. Most freelancers use prior-year safe harbor as the default and adjust to current-year only when income drops materially.
Your situation
Recommended method
Income rising (current year > prior year)
Caps obligation. You can owe a balance at filing without penalty.
Income falling (current year < prior year)
Avoids paying based on a higher year that no longer applies.
First year of self-employment
No prior-year tax baseline. Use a conservative income projection.
Income unpredictable / lumpy
Caps obligation regardless of current-year volatility.
Major drop in income mid-year
Form 2210 annualized installment recognizes when income arrived.
Form 1040-ES from the IRS is the official worksheet for both methods. Most tax software includes a quarterly estimate calculator that runs both calculations automatically.
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