Calculators that show their work
Plan early retirement, order the right amount of gravel, or find your zone 2 heart rate. Instant answers, honest assumptions and a clear explanation for every result.
● Money
All money calculators →Coast FIRE Calculator
See how much you need invested now to stop saving and let growth do the rest.
Open calculator →FIRE Calculator
Your financial independence number and the years it takes to reach it.
Open calculator →Mortgage Recast Calculator
New payment, interest saved and fee payback after a lump-sum recast.
Open calculator →Social Security Break-Even Calculator
Find the age where delaying Social Security pays off, e.g. 62 vs 70.
Open calculator →● Home & Yard
All home & yard calculators →● Fitness
All fitness calculators →Why CalcKeep
Math you can check
Every calculator lists its formula and a worked example, so you know exactly where the number comes from.
Private by design
Calculations run in your browser. Nothing you type is sent to us or stored on a server.
Fast on any device
No sign-ups, no heavy apps. Pages load quickly on phones and work in light or dark mode.
Tested and reviewed
Formulas are checked against known results and official rules, like SSA claiming reductions.