Tools
Estimated tax: the safe harbor
The least you need to have paid during the year to avoid the underpayment penalty, federal and California, and how it splits across the four payments. Nothing you type leaves this page.
Last reviewed Oct 2026
This shows the rule, not your tax. It does not work out what you will owe — put in Kit’s figures or your own.
Federal (IRS)
Enter this year’s expected tax to see the result. If you tick the box, also enter last year’s tax and AGI (for California, this year’s AGI too): the AGI decides whether 100% or 110% applies.
California (FTB)
Enter this year’s expected tax to see the result. If you tick the box, also enter last year’s tax and AGI (for California, this year’s AGI too): the AGI decides whether 100% or 110% applies.
Exact dates, moved for weekends and holidays, are on the deadline calendar. Tax deadlines →
The rule
Federal (IRS)
Pay the smaller of 90% of this year’s tax or 100% of last year’s (110% if last year’s AGI was over $150,000, or $75,000 if married filing separately), in four equal installments. Last year’s return must cover all 12 months. “Tax” here is total tax less refundable credits. No penalty if you owe less than $1,000 after withholding. No estimated payments are needed if last year’s tax was zero, you were a U.S. citizen or resident all year, and that year covered 12 months.
California (FTB)
The same 90% / 100% / 110% rule on California figures, but in installments of 30%, 40%, 0% and 30%, with a $500 threshold ($250 if married filing separately). If this year’s California AGI is $1,000,000 or more ($500,000 if married filing separately), only 90% of this year’s tax counts. The same applies if you did not file a California return last year, or it covered less than 12 months. If last year’s California tax, after credits, was under $500 ($250), the penalty does not apply.
Not covered here: farmers and fishermen, fiscal years, the annualized income method for uneven income, and payments made late. Talk to Kit about any of these.
Sources
Let’s start with a conversation
Want Kit to look at your own situation?
The first meeting to start a service is free. If you have last year's return, bring it: most people leave knowing what they need and what it will cost.