Loan payment (PMT)
For principal P, monthly rate r = APR/12/100, n months: PMT = P r (1+r)^n / ((1+r)^n − 1). If r = 0, PMT = P / n. Extra principal shortens n; biweekly uses 26 half-payments and rate/26.
Compound interest
FV = P (1 + r/m)m t plus future value of regular contributions. m is compounds per year.
Tax sketch
Federal pages apply simplified 2025-style brackets and a standard deduction. No credits, AMT, or state tax. Not a filing.
FAQ
APR vs APY?
Loan pages take a nominal annual rate divided by 12 unless labelled otherwise.
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