Quarterly Estimated Tax Calculator

The Quarterly Estimated Tax Calculator builds your US estimated-tax year the way the IRS expects it to be built: project the full year's income tax and self-employment tax, apply the safe-harbor rules against last year's liability, and divide what you must pay into four quarterly installments with their due dates. It is designed for freelancers, sole proprietors, and anyone with significant income that no employer withholds on.

How It Works

Self-employment tax is computed on 92.35% of net self-employment income: Social Security at 12.4% up to the wage base the calculator stores ($184,500 for 2026, reduced by any W-2 wages already taxed), Medicare at 2.9$150,000. Divide by four for the quarterly figure.

$\text{Quarterly payment}=\frac{\min\left(90\%\times\text{This year's tax},\ \text{Safe harbor from last year}\right)}{4}$

Parameters

| Input | Required | Meaning | |---|---|---| | Estimated annual / SE income | Yes | Projected income for the year | | Estimated deductions | No | Deductions reducing taxable income | | Filing status | Yes | Selects brackets and thresholds | | Net self-employment income | No | The SE-tax base figure | | W-2 wages | No | Wages already subject to Social Security tax | | Prior-year liability and AGI | No | Enables the safe-harbor comparison |

Worked example

A single freelancer projects $80,000 of net self-employment income and$20,000 of deductions. SE tax: the base is 80,000 x 92.35% = $73,880; Social Security takes 12.4$9,161.12) and Medicare 2.9% ($2,142.52), totalling$11,303.64. Income tax on $60,000 of taxable income (income minus deductions entered) under the stored single brackets is about$8,253. Total estimated tax is about $19,557; 90$17,601, so each quarterly payment is about **$4,400** if no lower safe harbor applies. If last year's liability was$14,000 on AGI under $150,000, the safe harbor would cap the required total at$14,000 instead, $3,500 a quarter, with the balance settled at filing: the safe harbor protects you from penalties, not from the final bill.

The due dates are not quarterly in the way you expect

The four installments fall on April 15, June 15 (only two months later), September 15, and January 15 of the following year. The uneven spacing, especially the short second period, ambushes new freelancers every June. The payments also cover uneven income awkwardly: if your income arrives late in the year, the annualized-income installment method lets you align payments with actual earnings and avoid overpaying early installments, at the cost of a more complex schedule this calculator does not generate.

Safe harbor strategy, and its limit

Paying the safe-harbor amount is the standard defensive play when this year's income is uncertain or spiking: it eliminates underpayment penalties even if the final bill is much larger, effectively an interest-free loan of the difference until filing. It is not a cap on tax owed, and the balance due in April can be brutal if a banner year was paid at last year's modest safe harbor without setting the difference aside. The discipline that makes the strategy work is reserving a fixed percentage of every receipt (many freelancers use 25 to 30%) in a separate account and letting the estimates draw from that, never from operating cash.

Limitations

The calculator uses stored simplified federal brackets and the 2026 SE parameters described above. It does not model state estimated taxes (most states with an income tax run their own quarterly system), the annualized installment method, credits, the qualified business income deduction's effect on income tax, or mid-year income changes. Estimates are planning figures; your tax software or preparer produces the filing-grade numbers, and the IRS rules for the current year govern.

Frequently Asked Questions

Who actually has to pay estimated tax?

Anyone expecting to owe at least $1,000 after withholding and credits, most commonly the self-employed, landlords, investors with large gains, and retirees with pension or IRA income not withheld on. W-2 employees can often solve the same problem by increasing withholding instead, which is treated as paid evenly through the year even if adjusted late.

What happens if I underpay a quarter?

An underpayment penalty, computed as interest on the shortfall for the period it was late, assessed quarter by quarter. The safe harbor exists precisely to make this avoidable: meet it and penalties do not apply even if the final liability is far higher.

Should I pay 90% of this year or 100% of last year?

Whichever is lower and defensible; the calculator compares them when you provide last year's figures. In a falling-income year, this year's 90% usually wins; in a rising-income year, last year's safe harbor usually does.