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On this site
These three run on kdp.cool. Each page shows the formula, the sources, and what the result does not include.
Monthly principal and interest, plus a simple tax and insurance draft. The $400,000 example is also written out below.
Federal brackets, FICA, an optional flat state rate, and pretax deductions, split across pay periods.
2026 ordinary brackets from IRS Revenue Procedure 2025-32, stacked one band at a time.
Static math, no JavaScript required
Two short cases you can check with a calculator. The longer write-ups live in Guides.
20% down, 6.5% annual rate, 30 years. Principal is $320,000. The standard amortizing formula gives monthly principal and interest of $2,022.62. Add $5,000/year property tax ($416.67) and $1,500/year insurance ($125) and the housing draft is $2,564.28.
Month 1 interest is $320,000 × 0.065 / 12 = $1,733.33, so only $289.28 goes to principal. That split is why early payments feel interest-heavy.
Single filer, biweekly, no state income tax, no 401(k), tax year 2026. Taxable income is $72,000 − $16,100 = $55,900. Federal tax stacks as $1,240 + $4,560 + $1,210 = $7,010. FICA adds $4,464 Social Security and $1,044 Medicare.
Estimated take-home is $59,482 a year, or about $2,287.77 every other week — closer to 17% combined federal-plus-FICA than to a flat 22%.
Scope
For the longer versions of the two examples above, plus guides on term tradeoffs, prepayments, FICA versus ordinary tax, 401(k) deferrals, and marginal versus effective rates, start at kdp.cool/guides.
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