This page lists, tool by tool, the formula or official figures behind each money and tax calculator on Anchor AI Tools, where the numbers come from and when each page was last updated.
By Amara Taylor · Last updated October 8, 2026
Each calculator applies the standard published formula or the official figure for its subject, and its output is checked against hand-worked examples before the page goes live. The arithmetic is dependable. Whether the result fits your situation depends on your inputs, because a calculator gives an estimate for planning, not tax, legal or financial advice.
The table covers the finance tools whose method is documented on their own page. More rows are added as each tool’s notes are checked.
| Calculator | What it calculates | Formula or method | Source of figures | Page last updated |
|---|---|---|---|---|
| Mortgage Calculator | Monthly principal-and-interest payment and total interest | M = P × [r(1+r)^n] ÷ [(1+r)^n − 1], where P is the loan amount, r the monthly rate (annual rate ÷ 12) and n the number of monthly payments | Standard amortization formula. No external data table. | September 25, 2026 |
| Payroll Calculator | Take-home pay per paycheck | Federal income tax from the seven 2026 brackets on pay after the standard deduction, plus Social Security and Medicare (FICA) | IRS Revenue Procedure 2025-32 for brackets and standard deduction | September 25, 2026 |
| Bonus Tax Calculator | Net bonus after withholding | Flat-rate method: 22% federal on supplemental wages up to $1,000,000 and 37% above; Social Security at 6.2% up to what remains of the 2026 wage base; state tax | IRS supplemental wage guidance and the Social Security Administration | September 25, 2026 |
| NY State Tax Calculator | New York income tax for 2025 or 2026 | Tax = sum of (income in each bracket × that bracket’s rate), after the New York standard deduction | NY Department of Taxation and Finance | September 25, 2026 |
| Michigan Property Tax Calculator | Annual and monthly property tax | Taxable value multiplied by the local millage, with the 50% assessment ratio, Proposal A and the homestead exemption applied | Michigan Department of Treasury guidance on Proposal A and the principal residence exemption | September 25, 2026 |
| Tax Refund Calculator | Federal refund or balance due for 2025 and 2026 | Refund = payments − total tax. Total tax = bracket tax on taxable income, less credits. Child tax credit of $2,200 per child, partly refundable up to $1,700 | IRS Revenue Procedure 2025-32, IRS federal income tax rates and brackets, IRS 2025 tax law changes | October 8, 2026 |
“Page last updated” is the date the page was last edited. Where a page depends on yearly figures, it names the tax year on the page itself.
The full process is on the editorial standards page. In short, each tool starts from the published formula, is tested by hand against example cases including zero values and rounding boundaries, and shows its working on the page.
Tax brackets, standard deductions, credit amounts and wage bases are taken from the agency that publishes them, such as the Internal Revenue Service and the Social Security Administration. State tools use the state revenue or treasury department. Pages built on these figures name the source and the year they apply to, and are revisited when the agency publishes new numbers.
A calculator only sees what you type in. It does not know about credits you did not enter, income you left out, or rules that apply to your circumstances alone. For a decision that matters, such as filing a complicated return, check with a qualified professional or the relevant agency.
| Date | Change |
|---|---|
| October 8, 2026 | Added the Tax Refund Calculator with 2025 and 2026 federal figures from IRS Revenue Procedure 2025-32 and IRS rate and credit pages. Published this methodology page. |
If a result looks wrong or a figure is out of date, write to hello@anchoraitools.com with what you entered and what you expected. Confirmed errors are corrected and the update log above records the change. You can read about who builds the tools on the about page.
Last updated: October 8, 2026 · Maintained by Amara Taylor, Content Lead, Anchor AI Tools.