Penny Runs the Numbers
Money calculators that show the math. Move the sliders, see the real numbers, check the sources.
Calculators
50-year vs 30-year mortgageCompare a 50-year and a 30-year mortgage: monthly payment, total interest and what you still owe after 10 or 30 years. Move the sliders, see the real math.Open calculator →Coast FIRE calculatorFind your Coast FIRE age: the first birthday at which your invested savings can grow on their own to your FIRE number by retirement. Move the sliders for age, savings, return and spending.Open calculator →Keep a 3% mortgage or move?Keep your low-rate mortgage or sell and buy at today's rate? See the new payment, the break-even rate, the downsizing price that keeps your payment, and how far behind moving puts you year by year.Open calculator →How much car can I afford?Enter your salary, loan APR and loan length to see the most car the 20/4/10 rule allows, the total interest, and what salary the average new-car loan really needs.Open calculator →How much house can I afford?Enter your salary and see the maximum home price under the 28/36 rule or Fannie Mae's 36%, 45% and 50% debt-to-income limits, with property tax, insurance and PMI included.Open calculator →Lottery lump sum vs annuityCompare a lottery cash option with the 30-payment annuity after federal and state tax, see the April tax bill, and find the return the lump sum needs to win.Open calculator →Retire early: 10,000 simulated retirementsTest an early retirement on 10,000 simulated futures built from real US stock and bond returns since 1928, after inflation. See your success rate, what's left at the end and the spending that keeps you 90% safe.Open calculator →Salary vs inflationWhat is a salary from 1970-2025 worth today, and did your raise beat inflation? Official BLS CPI-U data, plus how typical full-time pay grew over the same years.Open calculator →Cost of skipping your 401(k)What does pausing your 401(k) cost? Enter your salary, match and years skipped: see the lost match, the cost at retirement, the extra years of work, and how big a market crash it would take for skipping to win.Open calculator →
Free, honest money calculators: mortgages, retirement and everyday money questions. Every number comes from a model you can test with sliders, with sources listed. New calculators every week, each with a video by Penny.