How the engine works

Looking for a quick answer? Common questions are in the FAQ.

The simulation runs month by month from today until you reach age 90 (for a couple, until the younger of you does), and always at least 10 years. Growth compounds monthly using (1 + annual)^1/12 − 1; debts amortize at APR ÷ 12 the way real loans do, so you can cross-check any month against your actual statement.

Loan payments stay at the fixed amounts your lender charges; they don't rise with inflation. That's how real loans work, and it keeps every month matching your statement.

Debt payoff strategies: avalanche attacks the highest APR first (mathematically optimal); snowball attacks the smallest balance first (fastest first win). Freed-up minimum payments roll into the accelerant pool either way.

Social Security estimates use the bend-point formula with admin-updated bend points, adjusted for your claiming age. They remain rough — always verify at ssa.gov. Spousal and survivor benefits are not modeled.

Rather see it than read about it? The Strategy Sandbox runs the real engine on a worked example — change the numbers, watch every month move. No account needed.