SIT tax is state income tax — the amount your employer withholds from each paycheck and sends to your state government to pay for services like schools, roads, and law enforcement. Forty-two states collect some form of individual income tax, with rates that run from about 2% up past 13% depending on where you live and how much you earn. What you actually owe depends on your state’s rate structure, where you live, where you work, and the withholding form you filed with your employer.
How SIT Withholding Works
State income tax runs in parallel with federal income tax but stays inside your state’s budget. When you start a job, you fill out a state withholding certificate. Your employer uses the filing status and allowances you claimed on that form to calculate how much to deduct from each check, then remits the money to the state on your behalf.
States pick one of two rate structures:
- Flat tax. Every earner pays the same percentage. Roughly a third of the states with an income tax use a single flat rate, generally between 2% and about 5%.
- Progressive tax. The rate rises with income across a series of brackets. The lowest brackets start near 2%, and the highest marginal rate in the country reaches 13.3%.
Either way, the mechanics on your end are the same. Your employer does the math from the certificate you filed, and the withheld amount shows up as a line on your paystub.
States That Don’t Withhold SIT on Wages
Nine states do not tax wages and salary:
- Alaska
- Florida
- Nevada
- New Hampshire
- South Dakota
- Tennessee
- Texas
- Washington
- Wyoming
Washington is a partial exception: it applies a graduated tax to long-term capital gains, not to wages. New Hampshire used to tax interest and dividends but repealed that tax starting in 2025. If you live in one of these nine states, you generally won’t see a home-state SIT line on your stub, though you can still owe income tax to another state where you actually perform work.
If You See SIT on a Philadelphia Tax Form
In Philadelphia, “SIT” doesn’t mean the same thing it means on a paystub elsewhere. Philadelphia’s School Income Tax is a local tax on unearned income like dividends, certain interest, and short-term capital gains, at a rate of about 3.75%, with the money going to the school district. If the SIT you’re looking at is on a Philadelphia tax document rather than a wage stub, it refers to that school district levy, not Pennsylvania’s statewide income tax.
Which State Gets to Tax Your Income
Two ideas control who gets to tax you: where you live and where the income came from. Both can apply at the same time.
Your domicile is your permanent legal home, the place you intend to return to even when you’re away. Your domicile state taxes all of your income, from any source, wherever you earned it. Moving away temporarily doesn’t change your domicile. To establish a new one you generally have to build real ties: register to vote, get a driver’s license, and spend most of your time there.
Source-based taxation lets a state tax income earned inside its borders even if you live somewhere else. Cross state lines to work, or travel in for an assignment, and that state can claim a share of your wages for the days you worked there.
Many states also apply a statutory residency rule: if you keep a home in the state and spend more than 183 days there during the year, they treat you as a full-year resident for tax purposes. The rule is aimed at people who claim domicile in a low-tax state while actually living most of the year in a higher-tax one. State tax agencies check residency claims by sharing data with federal authorities.1Internal Revenue Service. State Information Sharing
If you move mid-year, you’re a part-year resident in both states. Each state taxes what you earned while living there, plus any income sourced from that state during the rest of the year, and you file a part-year return in each.
Working in One State, Living in Another
Living on one side of a state line and working on the other exposes you to two tax systems. States use a few different mechanisms to sort this out, and the mechanisms don’t always fully prevent double taxation.
Reciprocal Agreements
Some neighboring states have reciprocal agreements. If yours does, you pay income tax only to the state where you live, your employer withholds only for your home state, and you skip filing a nonresident return in the work state. These agreements typically cover wages and salaries but not business or rental income.
Convenience of the Employer Rule
A handful of states use a “convenience of the employer” rule. Under it, the state where your employer’s office sits can tax your wages even if you work remotely from another state, unless your employer actually requires you to work from elsewhere. That can leave a remote worker taxed by both states on the same income, and not every state offers a credit that fully offsets it. If you work remotely for an out-of-state employer, check both states’ rules before you assume your home state is the only one with a claim.
Credit for Taxes Paid to Another State
When there’s no reciprocal deal, most states let you claim a credit on your home-state return for income tax you paid to another state. The credit is usually capped at the lesser of what you paid the other state or what your home state would have charged on that same income. That prevents full double taxation in most cases but not always all of it.
Filling Out Your Withholding Certificate
Most states have their own withholding form, separate from the federal W-4. On it you list your filing status, the number of allowances you’re claiming, and any extra amount you want withheld each pay period. More allowances mean less tax pulled from each check; fewer allowances mean more. The form’s built-in worksheet walks you through the right number based on your credits, deductions, and personal situation.
Update the certificate whenever your life changes. A marriage, a new child, or a second job can throw off your withholding enough to leave you with a surprise balance due at filing time.
Don’t cheat the form. Filing a false withholding statement that lowers the tax deducted from your pay carries a $500 civil penalty per occurrence under federal law.2Office of the Law Revision Counsel. 26 USC 6682 – False Information With Respect to Withholding Willfully filing a fraudulent tax document is a felony punishable by up to three years in prison and fines up to $100,000.3Office of the Law Revision Counsel. 26 USC 7206 – Fraud and False Statements
Paying SIT Yourself: Estimated Payments
If you’re self-employed, live off investment income, or otherwise earn money that no employer withholds from, you owe state tax directly, in quarterly installments. The deadlines generally track the federal schedule in April, June, September, and January of the following year.4Internal Revenue Service. Estimated Taxes Most states run online portals for electronic payment from a bank account, and you can mail a check with a voucher if you prefer.
Federal safe harbor rules say you avoid an underpayment penalty if you pay at least 90% of your current-year liability or 100% of the tax shown on your prior-year return, whichever is smaller. That prior-year figure climbs to 110% if your adjusted gross income was over $150,000 the year before, or $75,000 if you file married separately.5Office of the Law Revision Counsel. 26 USC 6654 – Failure by Individual to Pay Estimated Income Tax You also stay out of penalty territory if you owe less than $1,000 after withholding and credits.6Internal Revenue Service. Underpayment of Estimated Tax by Individuals Penalty Most states follow a similar framework, though the exact thresholds vary.
If your income swings through the year, as it does for freelancers, seasonal workers, and investors, you can often cut penalties by annualizing income and paying unequal quarterly amounts that track when you actually earned the money.
What Happens If You Underpay or Pay Late
Falling behind on state income tax triggers penalties plus interest. The federal failure-to-pay penalty is 0.5% of the unpaid balance for each month it stays unpaid, capped at 25% of the balance, with interest running on top.7Internal Revenue Service. Failure to Pay Penalty State penalty structures vary but tend to follow a similar pattern, with combined rates that can reach 10% or more depending on the state and how long the balance sits.
Keep proof of every payment. The IRS recommends holding tax records at least three years, which lines up with the standard audit window.8Internal Revenue Service. How Long Should I Keep Records Some states use a longer window, so if your state pushes past three years, match its rule instead.