Personal Finance & Estate › Income, gift, estate & real-estate taxes › Income tax (federal & California)
Quarterly estimated taxes & safe harbors
Pay-as-you-go since 1943· Tax rule
Law or rule (2026)Set by statute, regulation or the agency; numbers change yearly.
Quarterly prepayments of income tax on income with no withholding, such as rents, K-1 income, gains and interest.
See it on the Personal Finance & Estate map →How it works
Federal estimates are due April 15, June 15, September 15 and January 15. You avoid penalties by paying 90% of this year's tax or 100% of last year's (110% if last year's AGI topped $150,000). California front-loads: 30% in April, 40% in June, none in September, 30% in January, and filers with income of $1 million or more can't use last year's tax as a safe harbor. Withholding counts as paid evenly, so extra year-end withholding can cure a shortfall.
Why it matters for you
Penalties are interest charges, not disasters, but a big sale or K-1 surprise can trigger them; ask your CPA to reset estimates after any large transaction.
Think of it like
Like monthly CAM estimates with a year-end reconciliation: pay enough along the way and there is no penalty.
Rules, limits and sources (2026)
The Current Tax Payment Act of 1943 created pay-as-you-go withholding; IRC Sec. 6654 and IRS Form 2210 set the safe harbors; California Form 5805 covers state rules.
Connections (2)
▸Quarterly estimated taxes & safe harbors prepay Income tax (federal & California)Law or rule (2026)
How they connect
Income tax is pay-as-you-go: wages are withheld, but rents, K-1 income, interest and gains usually aren't. Quarterly estimates fill that gap so the year's tax is mostly paid by January. Meeting a safe harbor prevents underpayment penalties even if a large balance is still due in April.
When it applies
Pay-as-you-go began with the Current Tax Payment Act of 1943, as wartime income tax spread to most workers.
The rule
IRC Sec. 6654 imposes the underpayment penalty; IRS Form 1040-ES and Publication 505 explain the safe harbors.
Watch out for
Whether to pay exactly the safe harbor or closer to actual tax depends on cash needs and interest rates; it's a judgment call.
▸Quarterly estimated taxes & safe harbors are paid quarterly to Internal Revenue Service (IRS)Law or rule (2026)
How they connect
With no withholding on rents, K-1 income and gains, the IRS expects tax as you earn it. Estimates go through IRS Direct Pay, EFTPS or your online account, and Form 2210 computes any underpayment penalty, which works like interest at the IRS rate, recently about 7% a year.
When it applies
Pay-as-you-go collection began with the Current Tax Payment Act of 1943, when wartime withholding started; quarterly estimates cover income that withholding misses.
The rule
IRC Sec. 6654 sets the underpayment penalty and safe harbors; Form 1040-ES gives the due dates and worksheets.
Watch out for
Many filers don't know the annualized method (Form 2210, Schedule AI) can cut penalties when income arrives late in the year; how often it's missed is unknown.