The first time a founder owes real quarterly taxes is usually the first time they’ve made real money — which means it’s also the first time getting it wrong is expensive. Payroll withholds automatically for W-2 employees. Nothing withholds for you. If you’re running an LLC, a sole proprietorship, or drawing distributions from an S-Corp on top of salary, the IRS expects you to send in your own tax payments four times a year — and it charges interest on the difference if you guess low.
The system is simpler than it looks once you separate the parts: who has to pay, when, how much, and what happens if you’re wrong.
Who Actually Has to Pay
You generally owe quarterly estimated taxes if both of these are true:
- You expect to owe $1,000 or more in federal tax for the year after subtracting withholding and refundable credits.
- Your withholding and credits won’t cover at least 90% of this year’s tax, or 100% of last year’s (110% if last year’s income was high — see the safe harbor section below).
For founders, this almost always means: any year your business has real net profit and nobody is withholding tax on it. That covers single-member LLC owners, multi-member LLC partners, S-Corp owners on the distribution portion of their income, and sole proprietors. If you’ve elected S-Corp status and pay yourself a proper salary through payroll (see our LLC vs. S-Corp math), your salary already has withholding — but your distributions still don’t, and neither does the corporate-level profit if you’re leaving cash in a C-Corp for personal tax purposes.
The 2026 Due Dates
Estimated taxes run on a quarterly schedule that doesn’t line up neatly with calendar quarters — “Q3” is only two months long:
| Payment period | Covers | Due date |
|---|---|---|
| Q1 | Jan 1 – Mar 31 | April 15, 2026 |
| Q2 | Apr 1 – May 31 | June 15, 2026 |
| Q3 | Jun 1 – Aug 31 | September 15, 2026 |
| Q4 | Sep 1 – Dec 31 | January 15, 2027 |
Payments go to the IRS with Form 1040-ES, either mailed with a voucher or paid directly through IRS Direct Pay or EFTPS — direct payment is faster and gives you an immediate confirmation number, which matters if a payment ever needs to be proven. Most states with income tax run a parallel schedule with their own form; check your state revenue department’s estimated-payment deadlines separately, since a few don’t match the federal dates exactly.
The Safe Harbor Rule: Your Actual Target
The number founders get wrong isn’t the due dates — it’s how much to pay. You don’t have to predict this year’s income precisely. The IRS gives you a fixed target, called the safe harbor, that protects you from a penalty regardless of how the year actually turns out:
- Pay 100% of last year’s total tax liability, split into four equal payments — safe, no matter how much you make this year.
- If your prior-year adjusted gross income was over $150,000 ($75,000 if married filing separately), the safe harbor rises to 110% of last year’s tax.
- Alternatively, you can pay 90% of this year’s actual tax as it becomes known — useful if last year was unusually high and you know this year will be lower, but riskier because it depends on correctly estimating a year that isn’t finished yet.
The practical move for most founders: take last year’s Form 1040 total tax line, multiply by 1.0 or 1.1 depending on your AGI, divide by four, and pay that amount each quarter. It’s the same total dollar target as trying to predict this year’s income exactly, without the guesswork — and if this year is a breakout year, the extra tax you owe isn’t due until you file, interest-free, as long as the quarterly safe harbor payments were made on time.
A Worked Example
A founder owed $42,000 in total federal tax last year, with an AGI under $150,000. The safe harbor payment:
$42,000 × 100% ÷ 4 = $10,500 per quarter
If this year’s business does dramatically better and the real tax bill turns out to be $68,000, no quarterly penalty applies — the $10,500/quarter payments satisfied the safe harbor. The founder owes the remaining $26,000 when they file, without interest on that gap, because each quarterly payment met the required threshold at the time it was due.
What Happens If You Underpay
Missing the safe harbor doesn’t trigger a flat fine — it triggers daily-compounding interest on whatever portion of each quarter’s payment was short, calculated from that quarter’s due date until it’s paid. The rate is set by the IRS each quarter, tied to the federal short-term rate plus 3 points, and it moves: it was 6% annualized in Q2 2026 and rose to 7% annualized for Q3 2026. IRS Form 2210 is what calculates the actual penalty if you underpaid, and most tax software fills it out automatically from your return.
Two things make this worse than founders expect:
- It’s calculated quarter by quarter, not for the year as a whole. Underpaying Q1 and overpaying Q4 to compensate still generates interest for the Q1 shortfall, because the IRS measures each period independently.
- There’s no grace for irregular income. A founder who closes a large deal in Q4 owes that quarter’s estimated tax by January 15 regardless of how thin Q1–Q3 were — unless they use the annualized income installment method (also filed via Form 2210), which lets seasonal or lumpy-revenue businesses calculate each quarter’s requirement based on actual income earned in that period rather than an even 25% split. It’s more paperwork, but it’s the correct tool if your revenue is genuinely front- or back-loaded.
Estimating the Number If You Don’t Have a Clean Prior Year
New founders — first year in business, or a year with a major income jump — don’t have a reliable prior-year baseline to run the safe harbor off of. In that case, build the estimate from the ground up:
- Project net profit for the year (revenue minus deductible business expenses).
- Apply self-employment tax: 15.3% on net profit up to the Social Security wage base ($184,500 for 2026), and 2.9% above it, plus an additional 0.9% Medicare surtax on self-employment income above $200,000 (single) or $250,000 (married filing jointly).
- Apply income tax at your marginal bracket on top of that — self-employment tax and income tax are separate calculations that both apply to the same net profit.
- Subtract the deduction for half of self-employment tax, which reduces the income-tax base (but not the SE-tax base itself).
- Divide the total by four.
This is exactly the calculation a CPA runs, and it’s also what tax software like TurboTax Self-Employed or a bookkeeper’s quarterly worksheet automates. If you’d rather work through the mechanics by hand once — so you actually understand what each payment is covering instead of trusting a black box — Barbara Weltman’s J.K. Lasser’s Small Business Taxes 2026 walks through the full estimated-tax worksheet line by line, alongside the deduction categories most founders miss in year one.
Adjusting Mid-Year
The safe harbor number isn’t locked in after Q1. If your business clearly outperforms or underperforms what last year’s tax bill implied, you can recalculate for the remaining quarters — there’s no rule requiring four identical payments, only that the cumulative amount paid by each due date meets the required threshold for that point in the year. A founder who signs a large contract in June can increase the Q3 and Q4 payments rather than carrying a large balance to filing season. Recalculating is also the right move the first time you cross into a materially different tax bracket, since a flat 25%-per-quarter split assumes your effective rate stays constant.
Where This Intersects With S-Corp Election
If you’ve elected S-Corp status, the picture splits in two: your salary already has federal and state withholding through payroll, so it doesn’t need a separate estimated payment. Your distributions — the profit paid out above salary — still aren’t withheld, and still need to be covered by quarterly estimates or by increasing your payroll withholding to cover the gap. Some founders prefer the latter: bumping withholding on the salary portion late in the year to cover the full liability, since withholding (unlike estimated payments) is treated by the IRS as paid evenly throughout the year no matter when it’s actually withheld. That’s a legitimate way to catch up in Q4 without a Q1–Q3 underpayment penalty, and it’s worth asking a payroll provider about if a big distribution is coming.
FAQ
What if I overpay?
You get it back as a refund when you file, or you can apply it to next year’s Q1 estimate. Overpaying has no penalty — it’s just an interest-free loan to the government, which is why the safe harbor target (not a padded guess) is the more efficient number to pay.
Do I need to make a payment every quarter, or just when I have income?
The default rule is four equal payments regardless of when income lands, unless you specifically use the annualized income installment method on Form 2210 to match payments to when income was actually earned. Skipping a quarter because “business was slow” without filing that method still exposes you to interest on the missed payment.
Can my accountant or bookkeeper just handle this?
Yes, and for most founders past the first year or two, that’s the right call — a CPA who already prepares your annual return can calculate the safe harbor number in minutes and set calendar reminders or auto-pay through EFTPS. The math above is worth understanding even if someone else executes it, because it’s the same math they’re using, and it’s the fastest way to sanity-check a number before you send four or five figures to the IRS.
Does this apply to state taxes too?
Most states with income tax have their own quarterly estimated payment system, often (but not always) mirroring the federal due dates and a similar safe harbor concept. States with no income tax — Texas, Florida, Wyoming, and a handful of others — have nothing to file here at the state level, though franchise or gross-receipts taxes in some of those states have their own separate deadlines.
Quarterly taxes aren’t a guessing game — they’re an arithmetic problem with a published safe harbor answer. Pull last year’s total tax, apply the right multiplier, divide by four, and set a calendar reminder for the four dates above. For the related structural decision that changes how much of your income needs this treatment in the first place, see LLC vs. S-Corp: The Tax Math Every Founder Should Run, or explore more on managing founder cash flow in the finance section on FutureSharks.
