How the student loan calculator works
The standard plan math
Federal loans default to a 10-year standard amortization — the same formula as any installment loan. It minimizes total interest but produces the highest payment, which is why extended (25-year) and income-driven plans exist. The trade is always the same shape: payment now vs interest total.
Income-driven plans, honestly
IDR plans (SAVE-era successors, IBR, PAYE lineage) cap payments near 5–10% of discretionary income and forgive balances after 20–25 years — life-changing for low incomes relative to debt, expensive for high incomes (small principal progress, growing interest). They are insurance against unaffordable payments, not a cheaper path — total cost usually exceeds standard payoff for graduates who can afford the standard payment.
The pre-loan decision that matters most
Every dollar saved before enrollment is a dollar that does not accrue 6.5% from day one — the 529's tax-free growth vs the loan's interest is roughly a 13-point swing on the same dollar. This is the arithmetic behind "the best student loan is a small one," and the reason the savings calculators on this site precede this one.