tax · 2026-05-01
Compute the minimum federal estimated tax payments to avoid the underpayment penalty — using the lesser of 90% of current year or 100/110% of prior year.
| Prior year total tax | $35,000 |
| Current year projected tax | $42,000 |
| Current year W-2 withholding | $5,000 |
| Prior year AGI | $175,000 |
| Total required payments | $32,800 |
| Safe harbor target | $37,800 |
| Prior year multiplier (100% or 110%) | 1 |
The IRS doesn't actually care if you owe at year-end — they care if you DIDN'T pay enough in real-time. The safe harbor lets you avoid the underpayment penalty by hitting the LESSER of two thresholds:
target = MIN(
prior year tax × (1.00 or 1.10),
current year projected tax × 0.90
)The 1.00 vs 1.10 toggle: if last year's AGI was over $150k, multiplier is 1.10 (110%). Below: 1.00.
For most freelancers / business owners with growing income: target prior year × 110%. It's locked in at filing time, easy to compute, no projection error.
For folks whose income drops year-over-year: target current year × 90%. Avoids overpaying when you'd otherwise pay 110% of a high prior year.
The IRS calculates the penalty as roughly the IRS short-term rate + 3% (currently ~8%) on the shortfall, prorated by quarter. For a $5k underpayment: $400-500 penalty. Annoying but manageable.
April 15, June 15, September 15, January 15 of next year. NOT evenly spaced months — Q1 is 3 months, Q2 is 2, Q3 is 3, Q4 is 4. The IRS uses a weird quarterly system. Pay equal amounts each due date for the simplest path; underpayment penalty calculates per-quarter.
Yes — and it's often easier. W-2 withholding is treated as paid evenly across the year regardless of when actually withheld. So a December W-2 withholding boost can retroactively cover a Q1 shortfall. This is the 'big year-end W-4 adjustment' move common for business owners with W-2 spouses.
Each state has its own. Most mirror federal: 100/110% prior or 90% current. Some states (CA, NY) have stricter or more frequent payment schedules. Calculate state separately — federal safe harbor doesn't protect from state penalty.