For self-employed owners, S-corp owners, and anyone whose income jumped this year

Your big year changed the Q4 math.

A practical worksheet to estimate a remaining payment target using the actual safe-harbor rules, not a generic percentage of income.

Built for income spike years: bonuses, equity comp, a profitable S-corp, a side business, or a big distribution.

What's inside

The two safe-harbor tests in plain English (100% / 110% of prior, or 90% of current)
The $150K AGI threshold and how withholding changes the math
Why W-2 withholding is treated differently than estimated payments
A nine-line worksheet to estimate the remaining required payment for your facts
When an extension does NOT save you from the penalty
The three moves that work in the last 60 days of the year

Send me the worksheet.

The penalty is small per dollar but ugly per surprise.

Estimated tax rules compare required payments with what was paid and when. The worksheet shows the general 90% current-year and 100% or 110% prior-year paths, then separates withholding from estimated payments.

This worksheet is built for self-employed owners, S-corp owners, and W-2 earners with bonus or equity income that pushed AGI past the prior-year baseline. It uses real numbers: prior-year liability, current-year projection, withholding to date, and Jan 15 deadline.

The goal is not to lower your tax. The goal is to avoid the underpayment penalty by sizing the Q4 voucher correctly and choosing between voucher, withholding bump, or both.

Withholding is generally treated as paid evenly during the year unless the taxpayer establishes actual withholding dates. That can make timing materially different from an estimated payment.

General information for safe-harbor planning. Not tax advice for your specific facts. Alex Sears CPA LLC is a Texas-licensed CPA firm.