If you’re a sole proprietor, a partner, an S corporation shareholder, or anyone else whose income doesn’t have taxes withheld from a paycheck, the IRS expects you to pay as you go. The second federal estimated payment of 2026 is due Monday, June 15 — and in California, the state payment due the same day is the largest one on the calendar.
Who actually owes estimates
The rule of thumb: if you expect to owe at least $1,000 in federal tax beyond what withholding covers, you’re in estimated-payment territory. That catches most business owners — profit that flows through a Schedule C, a partnership K-1, or an S corp K-1 has no withholding attached to it.
The safe harbors, in plain English
You don’t have to predict the year perfectly. Penalties go away if your payments through the year hit either target:
- 90% of this year’s tax — the right target if 2026 is shaping up slower than last year, or
- 100% of last year’s tax (110% if your adjusted gross income was over $150,000) — the set-it-and-forget-it target when this year looks flat or better.
Most of our clients use the prior-year safe harbor for predictability, then we true it up at the mid-year review when six months of real numbers exist.
The California twist: June is the big one
The FTB doesn’t split the year into four equal payments. California weights them 30% — 40% — 0% — 30%, which means the June 15 state payment is 40% of the whole year’s estimate — and there’s no payment due in September. Owners who assume “four equal quarters” routinely underpay June and eat a penalty that was completely avoidable. Our 2026 deadline calendar lays out every federal and California date for the year — September gap included — so nothing sneaks up on you.
Don’t copy your April payment and hit send. The federal and state amounts diverge in June — California wants more, and if business is up this year, both numbers probably moved. Ten minutes with year-to-date profit gets the number right; guessing gets you an underpayment penalty that currently accrues at an interest rate north of 7%.
Before June 15
- Pull year-to-date profit from your books (if your books aren’t current, that’s the real problem)
- Check which safe harbor you’re aiming for — 90% current-year or 100/110% prior-year
- Remember California’s 40% weighting — the state number is not the federal number
- Pay federal at IRS Direct Pay or EFTPS; pay California at FTB Web Pay
- Calendar the rest of the year: September 15 (federal only) and January 15
This article is general information, not tax advice for your specific situation. Rules change and details matter — talk to a CPA (we know one) before acting on anything here.