Everything written about the September 15 estimated-tax deadline is about the federal one. Your state runs its own system, with its own threshold, its own instalment schedule and its own safe harbor, and the differences are larger than most people assume. In California, the third instalment is zero.
If you have been budgeting a state payment for September, or ignoring one, it is worth twenty minutes to check which of those two mistakes you are making.
Tax Disclaimer: This article covers four states, each sourced from its own revenue department, and is not tax advice. Rules differ in every state and this is not a complete list. Consult a certified CPA or tax professional for individual advice.
California asks for nothing in September
California does not split the year into four equal parts. Its instalments run 30% due April 15, 40% due June 15, 0% due September 15, and 30% due January 15, 2027 (California Franchise Tax Board).
Read the shape of that. California wants the great majority of the year’s tax before the end of June, then nothing at all in September, then the balance in January. It is front-loaded in a way the federal schedule is not, and the consequences run in both directions.
If you assumed four even quarters, you underpaid California in April and June and you will not fix it by sending money in September, because the third instalment is already satisfied at zero. If you have been dutifully setting aside a quarter each time, you are holding a September payment California does not want, and the money is yours until January.
Two other California details worth knowing. The threshold is lower than the federal one: estimated payments are required if you expect to owe at least $500, or $250 if married or in a registered domestic partnership filing separately (California Franchise Tax Board). And the safe harbor tests mirror the federal shape, at 90% of the current year’s tax or 100% of the prior year’s (California Franchise Tax Board).
The thresholds are lower than the federal one everywhere it matters
The federal system ignores you until you expect to owe $1,000. No state on this list is that generous.
| State | You must pay estimated tax if you expect to owe | Q3 due |
|---|---|---|
| Federal | $1,000 | September 15 |
| New York | $300 of state, NYC or Yonkers tax (NY Form IT-2105-I) | September 15 |
| Pennsylvania | $430, roughly $14,000 of income not subject to withholding (PA REV-413I) | September 15 |
| New Jersey | $400 after withholdings and credits (NJ Division of Taxation) | September 15 |
| California | $500, or $250 if filing separately (California FTB) | 0% due |
The practical effect: a side income small enough to leave you clear of the federal requirement can still put you inside your state’s. New York starts at less than a third of the federal figure.
The safe harbor is not the same rule everywhere
New York’s mirrors the federal structure closely. You need 90% of the tax on your 2026 return, or 100% of the tax on your 2025 return, and that becomes 110% if your New York adjusted gross income on the prior return was more than $150,000, or $75,000 if married filing separately (NY Form IT-2105-I). Anyone who has already worked out their federal safe harbor can compute the New York one from the same two returns.
Pennsylvania’s is simpler and shaped differently: pay 100% of last year’s Pennsylvania tax, calculated from the taxable income on your 2025 PA-40, and you are protected, provided you filed a full-year resident return for 2025 (PA REV-413I).
The lesson is not the detail. It is that “I’ve covered my safe harbor” is a federal sentence, and it does not automatically mean anything about your state.
Nine states where the question does not arise
If you live in one of these, wage income is not taxed at the state level at all: Alaska (no state tax on wages), Florida (no state tax on wages), Nevada (no state tax on wages), New Hampshire (no state tax on wages), South Dakota (no state tax on wages), Tennessee (no state tax on wages), Texas (no state tax on wages), Washington (no state tax on wages (2026)) and Wyoming (no state tax on wages).
Your federal obligation is unchanged. There is simply no second calendar to track.
What to check before September 15
Four questions, in this order, and the first one settles it for a lot of people.
- Which state taxes this income? Generally where you performed the work, not where the client is. If you moved during 2026, you may owe two states part-year.
- What is that state’s threshold? It is probably lower than $1,000, and you may already be over it.
- What is that state’s Q3 percentage? Do not assume an even quarter. California’s is zero.
- What does its safe harbor ask for? Your federal calculation does not carry over.
Most state revenue departments publish all four answers on one page. The states above are the ones with the largest number of freelancers between them, not a representative sample: if yours is not here, look it up rather than inferring from a neighbour.
The bottom line
The federal deadline gets the coverage because it is one rule for everyone. The state layer is where the money quietly goes wrong, and it goes wrong in two opposite ways in the same week: Californians sending a September payment that is not due, and New Yorkers a little over the $300 line (NY Form IT-2105-I) who never realised they were in the system at all. Look up your own state’s threshold and its Q3 percentage before the 15th. It is one page on one website, and it is the difference between a clean quarter and a penalty notice next spring.
Work out the federal side first in the 1099 tax estimator, check it against the safe harbor number the IRS cannot penalise you for, then handle the payment itself through the right method and the right cutoff.
