Estimated Tax Calculator for Individuals and C-Corps (2026 and 2027)

Individuals generally must make estimated payments if they expect to owe $1,000 or more for the year after withholding and refundable credits (IRC §6654). That covers most people with self-employment income, S-corp distributions, large capital gains or equity sales without withholding.

Corporations must make estimated payments if they expect to owe $500 or more of tax for the year (IRC §6655). Most startups never reach that point because they run at a loss, but a profitable SaaS company, or one that loses R&D expensing on foreign research, can owe tax earlier than expected.

S corporations and partnerships generally do not pay federal income tax at the entity level. Their owners pay estimated tax personally on their share of profit.

For individuals, you avoid the penalty if withholding plus timely estimates equal the smaller of:

• 90% of your current-year tax, or
• 100% of the tax shown on your prior-year return, or 110% if your prior-year adjusted gross income was more than $150,000 ($75,000 if married filing separately)

The prior-year number is the one most founders use, because it is known in advance. If at least two-thirds of your gross income is from farming or fishing, different rules apply.

For corporations, the required annual payment is the smaller of 100% of current-year tax or 100% of prior-year tax. The prior-year option is not available if the prior year was shorter than 12 months or the corporation had no tax liability on its prior return, which rules it out for most newly profitable startups. A large corporation, one with $1,000,000 or more of taxable income in any of the three preceding years, can use prior-year tax only for its first installment.

The last individual payment for 2027 moves to January 18, 2028 because January 15, 2028 is a Saturday and January 17 is Martin Luther King Jr. Day. The 2027 dates follow the statute and the weekend and holiday rule; confirm them against the 2027 Form 1040-ES when the IRS releases it. Fiscal-year corporations pay on the 15th day of the 4th, 6th, 9th and 12th months.

You can skip the January 15, 2027 individual payment if you file your 2026 return by February 1, 2027 and pay the full balance with it.

A hypothetical founder had 2025 AGI of $200,000 and total tax of $40,000. She expects $60,000 of tax for 2026 because of a secondary sale.

• 90% of current year: $60,000 x 90% = $54,000
• 110% of prior year (AGI over $150,000): $40,000 x 110% = $44,000
• Required annual payment: the smaller, $44,000, or $11,000 per quarter

She still owes the remaining $16,000 in April 2027, but no penalty.

A hypothetical calendar-year C-corp owed $30,000 for 2025 on a full 12-month return and expects $50,000 for 2026. It is not a large corporation, so it can pay 100% of prior-year tax: $30,000, or $7,500 per installment, due April 15, June 15, September 15 and December 15, 2026. Had 2025 been its first, short tax year, it would need to pay based on 2026 tax instead.

If most of your income arrives late in the year, the annualized income installment method can lower the earlier payments. Individuals compute it on Form 2210, Schedule AI. Corporations use the annualized or adjusted seasonal methods on Form 2220.

The penalty works like interest. It is charged at the IRS underpayment rate under IRC §6621 (the federal short-term rate plus 3 percentage points, reset quarterly) on each installment's shortfall for the number of days it stays unpaid. Paying late is cheaper than not paying at all.

The calculator does not cover state estimated taxes, which use their own dates and percentages, nor the alternative minimum tax, the net investment income tax, or penalty waivers for casualty, disaster or retirement. It gives you a payment plan, not your final tax.

Individuals can pay through IRS Direct Pay, their IRS Online Account, EFTPS, or by debit or credit card, and should label each payment as a 2026 (or 2027) estimated tax payment for Form 1040-ES. Corporations pay through EFTPS or their IRS business tax account.

Keep a record of each confirmation number. Your preparer will need the dates and amounts to report the payments on your return and to compute any penalty on Form 2210 or Form 2220. This page is a planning estimate, not tax advice for your specific facts.