Quarterly estimated tax calculator

The safe-harbor method: pay 100% of last year's total tax (110% if your prior-year AGI topped $150,000) in four installments, and the IRS cannot charge you an underpayment penalty, no matter what you actually earn this year.

Last year's total tax (Form 1040, line 22)My prior-year AGI was over $150,000 (110% safe harbor applies)Tax already withheld this year, from a W-2 job, if any (optional)

Educational tool, not tax advice. The safe harbor protects against penalties, not against owing more in April if your income grew; confirm specifics with a CPA or enrolled agent.

The hard part isn't the math, it's knowing your actual profit. SmallBooks keeps your income and expenses current automatically, so numbers like this are always one report away. Free during early access.