Quarterly Estimates After You Extended

Filing an extension does not extend the time to pay tax due for the prior year. If you also earn income without withholding (self-employment, RSUs sold without enough withholding, large investment gains), you may owe quarterly estimated taxes for the current year even while you are still cleaning up last year’s return. This article explains safe harbors at a high level and how to avoid surprises.

TL;DR

Federal estimated taxes are generally due April 15, June 15, September 15, and January 15 (of the following year) for calendar-year taxpayers.
Safe harbors often include paying 90% of current-year tax or 100% / 110% of prior-year tax (depending on income); see Form 1040-ES instructions for the year you are in.
An extension for filing does not stop underpayment penalties for tax you owed in April.
Use Form 2210 only when your facts require it; many taxpayers rely on safe harbors through withholding + estimates.

What “extension” does not do

You requested extra time to file Form 1040. If you had a balance due for April, interest and failure-to-pay penalties may still apply from that date on the unpaid amount (subject to IRS calculations and exceptions).

Quarterly estimates: who pays them

Typical situations:

Schedule C profit with no withholding
Partnership K-1 income with insufficient withholding
Large capital gains without offsetting withholding
RSU vesting with supplemental withholding that still leaves a shortfall

Safe harbor snapshot (conceptual)

Tax law provides several ways to avoid underpayment penalties if you meet specific thresholds. Common patterns:

Pay at least 90% of the tax shown on the current-year return through withholding + estimates by the due date.
Or pay 100% (or 110% if AGI exceeds a threshold) of prior-year tax through withholding + estimates.

Exact percentages and thresholds change with tax law; always read the current-year Form 1040-ES and Publication 505.

Worked example: consultant with lumpy income

Q1–Q2 income is low; Q3 lands a $80,000 contract payment.

Without adjusting Q3 or Q4 estimates, January 15 may be painful.
Annualization (Schedule AI on Form 2210) may help if you qualify—ask a professional.

Document proof callout

Keep confirmation numbers for EFTPS or direct pay for each quarterly payment. Match them to Form 1040 Line 26 (estimated tax payments) when you file.

FAQ

Do states match federal quarters?
Often similar, but not identical. Check your state DOR site.

Can withholding from my job cover side income?
Sometimes yes if you raise W-4 withholding enough.

How to act on this today

Model your refund or balance with our refund estimator tool (illustrative), then register for full computation on your uploads. If last year’s return is still open, read extension and verify what you filed.

Educational content only—not individualized tax advice.