Corporate Estimated Tax Calculator
Work out each of your four federal installments at the 21% rate, with the required annual payment tested both ways and the large-corporation restriction applied where it bites.
Work out each installment
Federal corporate estimated tax at the 21% rate, with the required annual payment worked out both ways and the large-corporation rule applied where it bites. Installments are due on the 15th day of the 4th, 6th, 9th and 12th months of your tax year, so the dates follow your year end, not the calendar.
Taxable income after deductions, as it will appear on the return. Not revenue and not book income.
R&D credit, foreign tax credit, and any other credits you expect to claim. These reduce the tax the installments are based on.
You may base installments on this instead, but only if last year's return covered a full 12 months and showed tax due. Leave blank if either is untrue.
$1 million or more in any of the three preceding years makes you a large corporation, which restricts the prior-year method to the first installment only.
Installments fall on the 15th day of the 4th, 6th, 9th and 12th months of the tax year, so a June year end moves every date.
Estimated tax already deposited for this tax year, plus any prior-year overpayment you elected to apply.
Runs entirely in your browser. Nothing you enter is sent to us or stored.
Result
Installment 1, due April 15, 2026
$78,750
- Expected tax at 21%
- $420,000
- Less expected credits
- $0
- Expected tax for the year
- $420,000
- Required annual payment
- $420,000
- Basis used
- Last year for installment 1, this year after
- Large corporation
- Yes
- Federal only. States run their own corporate estimated tax, on their own dates.
- As a large corporation (taxable income of $1 million or more in any of the last three years) you may use last year's tax for the first installment only. The saving is added back to the second installment, which is why it is the largest.
- Corporations must deposit estimated tax electronically through EFTPS. A cheque is not an option.
- If your income is seasonal or arrives late in the year, the annualized income or adjusted seasonal installment method (Form 2220, Schedule A) can lower the earlier installments below the figures here.
Installment schedule
| Installment | Due | Amount |
|---|---|---|
| 1 | April 15, 2026 | $78,750 |
| 2 | June 15, 2026 | $131,250 |
| 3 | September 15, 2026 | $105,000 |
| 4 | December 15, 2026 | $105,000 |
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How corporate estimated tax works
A C corporation pays its federal income tax in four installments across the year, not in one payment at filing. The rules sit in section 6655, and they are not the individual rules with a different form on top: the rate, the dates and the safe harbours are all different from a 1040-ES calculation.
The rate is flat
Expected tax = Taxable income x 21% - credits
There are no brackets. Corporate income tax has been a flat 21% since the 2017 Act, and that is still the rate for 2026 (IRS Publication 542). Credits you expect to claim, the R&D credit included, come off before the installments are worked out, which is why an accurate credit estimate is worth real cash flow early in the year.
Under $500 you owe nothing quarterly. A corporation only has to make installments if it expects to owe $500 or more for the year.
The required annual payment, tested two ways
Required annual payment = the LESSER of
100% of this year's expected tax
100% of last year's tax
Note what is missing: the 110% step. That is an individual rule for higher-income filers and it does not apply to corporations. Applying it here would overstate every installment by a tenth.
The prior-year figure is conditional, and all three conditions have to hold: you filed a return for last year, it covered a full 12 months, and it showed a positive tax liability. A first-year corporation cannot use it. Nor can one that broke even, because a zero liability is not a positive one.
The large-corporation restriction
This is the rule most often missed, and it is expensive to miss.
A large corporation is one with taxable income of $1 million or more in any of the three preceding tax years. Note "any of the three": one good year three years ago still counts, even if the two since were thin, and it is taxable income that counts rather than revenue.
A large corporation may use the prior-year figure for the first installment only. The amount it saved by doing so is then recaptured: the second installment is increased by exactly that reduction. Installments three and four are plain quarters of the current-year figure. The four still add up to 100% of the current year's tax, so the concession is a timing benefit on one payment, never a reduction in what the year costs.
The dates follow your year end, not the calendar
Installments are due on the 15th day of the
4th, 6th, 9th and 12th months of the TAX YEAR
For a calendar-year filer that is April, June, September and December. For a June year end it is October, December, March and June. A date falling on a weekend or a federal holiday moves to the next business day.
Two things worth noting about the mechanics. Deposits must be electronic, through EFTPS; a corporation cannot post a cheque for estimated tax. And Form 1120-W is gone as a form: the 2022 revision was its last, and the worksheet now lives in the Form 1120 instructions and Publication 542. Form 2220 is what computes the penalty if the installments were short.
When the flat quarters are the wrong answer
The four-equal-installments approach assumes income arrives evenly. If yours does not, the annualized income installment method and the adjusted seasonal installment method (Form 2220, Schedule A) compute each installment from the income actually earned by that point. For a business that makes its year in the fourth quarter, they can cut the early installments substantially. They are more work, and they are the right answer for genuinely seasonal income.
A worked example
A calendar-year corporation expecting $2,000,000 of taxable income in 2026, no credits. Last year's tax was $315,000, and its highest taxable income in the last three years was $1,400,000.
| Step | Amount |
|---|---|
| Expected taxable income | $2,000,000 |
| Expected tax at 21% | $420,000 |
| Prior-year tax | $315,000 |
| Large corporation? | Yes, $1.4M is above the $1M threshold |
| Required annual payment | $420,000 |
Because it is a large corporation, the prior-year figure is available for the first installment only:
| Installment | Due | Amount |
|---|---|---|
| 1 | April 15, 2026 | $78,750 |
| 2 | June 15, 2026 | $131,250 |
| 3 | September 15, 2026 | $105,000 |
| 4 | December 15, 2026 | $105,000 |
Installment 1 is a quarter of last year's $315,000. A plain quarter of this year's tax would have been $105,000, so the first payment is $26,250 lighter, and that $26,250 is added straight back onto installment 2. The four still sum to $420,000.
Now change one input. Had the same corporation's three-year peak been $900,000 instead of $1.4M, it would not be a large corporation, the required annual payment would drop to last year's $315,000, and all four installments would be $78,750 each: $105,000 less across the year, deferred to the filing deadline. The large-corporation test is the single most consequential figure on the form.
What this calculator does not cover
This is a federal C-corporation estimate at the standard 21% rate.
It does not handle the annualized income or adjusted seasonal installment methods, the corporate alternative minimum tax on adjusted financial statement income (which applies to corporations averaging over $1 billion of adjusted financial statement income), state and local corporate estimated tax, consolidated-group allocations, short tax years, the personal holding company tax, or the accumulated earnings tax. It does not apply to S corporations or partnerships, which do not pay income tax at entity level, or to tax-exempt organisations with unrelated business income.
This calculator is an estimate for planning, not tax advice. It assumes the taxable income you entered is complete and does not know your full facts. Confirm your figures with a qualified tax professional before you deposit or file.
FAQs
On the 15th day of the 4th, 6th, 9th and 12th months of your tax year. For a calendar-year corporation that is April 15, June 15, September 15 and December 15. Note that the fourth installment falls in December, not in January of the following year as it does for individuals. A due date landing on a weekend or federal holiday moves to the next business day.
A quarter of the required annual payment, which is the lesser of 100% of this year's expected tax and 100% of last year's tax. There is no 110% version of the prior-year rule for corporations, and the prior-year option is only available if last year's return covered a full 12 months and showed tax due.
Taxable income of $1 million or more in any of the three preceding tax years. It matters because a large corporation loses the prior-year safe harbour for everything except its first installment, and the saving on that first installment is added back to the second. One strong year three years ago is enough to trigger it, and it is taxable income that counts, not revenue.
Yes, if you expect to owe $500 or more. What you cannot do in year one is use the prior-year safe harbour, because there is no prior-year return covering 12 months with a positive liability. That makes a first-year corporation entirely dependent on the accuracy of its own income projection, which is the case where the annualized income installment method is most often worth the extra work.
The IRS charges an addition to tax on the shortfall, computed for the period it was unpaid at the published quarterly interest rate. Form 2220 works it out. Unlike some penalties it cannot be abated for reasonable cause, so it is worth getting the installments right rather than arguing afterwards.
Yes. Credits come off before the installments are computed, so a credit you are confident of reduces every quarterly deposit rather than turning up as a refund after filing. That is a real cash-flow difference across a year, and it is the main reason to have the credit study done early rather than at filing.
No. Corporations must deposit federal estimated tax electronically through EFTPS. Enrolment takes a few days, so it is worth doing before the first installment rather than the week of it.
No, this is federal only. Most states levy their own corporate income or franchise tax with their own installment dates, their own safe harbours and, in several cases, their own definition of taxable income. Add yours on top of these figures.
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