Browser-only practice economics · no account
What do you send the IRS and the FTB, and when?
Enter this year’s expected profit and last year’s tax. The page applies both safe harbors — the lesser of 90% of this year or 100% (or 110%) of last year — and lays out the four federal payments and California’s 30–40–0–30, dated.
Your numbers →Your numbers
Two figures from this year, three from last year’s returns.
Profit is collected fees less practice costs, before any tax, as a sole proprietor. Last year’s tax is the total tax line on each return — federal Form 1040 (including self-employment tax) and California Form 540 — and last year’s adjusted gross income decides whether the prior-year harbor is 100% or 110%. Withholding is anything a W-2 job takes out this year; it counts toward the harbor. Married filing separately is not modeled here.
The eight dates
Four federal, four California — and the September one is different.
| Due | Federal (1040-ES) | California (540-ES) | Together |
|---|---|---|---|
| 15 April 2026 | — | — | — |
| 15 June 2026 | — | — | — |
| 15 September 2026 | — | — | — |
| 15 January 2027 | — | — | — |
Federal installments are equal quarters of the required amount. California asks for 30% in April, 40% in June, nothing in September and 30% in January. A due date that falls on a weekend or holiday moves to the next business day; check the form for the year.
How it computes
Two harbors, one cliff, and the lesser of each.
Self-employment tax on 92.35% of profit, half of it deducted, the 20% qualified business income deduction with its phase-out, then the 2026 federal schedule and the 2025 California schedule — the same engine as every other money page here. Federal “tax” for the harbor includes self-employment tax, because Form 1040 does.
If last year’s adjusted gross income was above $150,000, the prior-year figure is 110%. Withholding is subtracted. If under $1,000 remains, no estimates are required and the page says so. Four equal installments.
100% of last year, or 110% above $150,000 of AGI, against 90% of this year — but at $1,000,000 or more of current-year California AGI the prior-year harbor is gone and 90% of this year is the floor. Estimates are required at $500 or more after withholding. Then the 30–40–0–30 split.
Paying the harbor amounts on time avoids the underpayment penalty. It does not settle the year: if this year’s tax is higher than the harbor, the difference is due with the return. A first year with no prior-year tax has only the 90% anchor.
Then what
The plan is the floor. The rest of the tax decision sits on these pages.
The rules, explained
Why California asks for 30, 40, 0 and 30
The article this calculator is built on: the schedule, the harbors, the penalty and what happens in a first year.
Lowering the number itself
Retirement accounts and the S corporation question
Estimates follow the tax; the tax follows the structure and the contributions. Same constants.
What is deductible
What a California therapist can deduct
Profit is fees less real practice expense; this page is what counts.
Lowering the tax the harbor measures
The retirement contribution calculator
SEP, solo 401(k) and SIMPLE on this profit; a contribution lowers this year’s tax and so the plan above.
Where every figure came from
Sources.
The rules
The engine
The constants are the ones the practice simulator and the tax-strategy page use, copied rather than restated. Married filing separately is not modeled.
