{"tool":{"slug":"compound-interest","name":"Compound interest calculator","version":"2026-08-21","canonicalUrl":"https://carlo.finance/tools/compound-interest","jsonUrl":"https://carlo.finance/tools/compound-interest.json","pageUrl":"https://carlo.finance/tools/compound-interest","parameters":[{"key":"principal","label":"Starting amount","unit":"usd","min":0,"max":100000000,"default":10000,"sourceId":null,"help":"What you start with. The default is an example, not a statistic."},{"key":"monthly","label":"Monthly contribution","unit":"usd-per-month","min":0,"max":1000000,"default":250,"sourceId":null,"help":"Added at the end of each month. The default is an example; set it to zero to grow the starting amount alone."},{"key":"rate","label":"Annual return","unit":"percent","min":0,"max":20,"default":7,"sourceId":null,"help":"The yearly growth you assume, before taxes and fees. This is an assumption you choose, not a forecast; the default is an example to replace with your own."},{"key":"years","label":"Years to grow","unit":"years","min":1,"max":60,"default":20,"sourceId":null,"integer":true,"help":"How long the money compounds before you look at the balance."},{"key":"compounds","label":"Compounding per year","unit":"count","min":1,"max":365,"default":12,"sourceId":null,"integer":true,"help":"How many times a year interest is credited: 1 yearly, 12 monthly, 365 daily."}]},"inputs":{"principal":10000,"monthly":250,"rate":7,"years":20,"compounds":12},"result":{"endBalance":170619.05,"totalContributed":70000,"growth":100619.05,"effectiveAnnualYield":7.229,"doublingYears":9.931,"months":240,"finalYearGrowth":11391.82,"yearly":[{"year":1,"contributed":13000,"growth":821.05,"balance":13821.05},{"year":2,"contributed":16000,"growth":1918.32,"balance":17918.32},{"year":3,"contributed":19000,"growth":3311.78,"balance":22311.78},{"year":4,"contributed":22000,"growth":5022.85,"balance":27022.85},{"year":5,"contributed":25000,"growth":7074.48,"balance":32074.48},{"year":6,"contributed":28000,"growth":9491.29,"balance":37491.29},{"year":7,"contributed":31000,"growth":12299.69,"balance":43299.69},{"year":8,"contributed":34000,"growth":15527.97,"balance":49527.97},{"year":9,"contributed":37000,"growth":19206.5,"balance":56206.5},{"year":10,"contributed":40000,"growth":23367.82,"balance":63367.82},{"year":11,"contributed":43000,"growth":28046.83,"balance":71046.83},{"year":12,"contributed":46000,"growth":33280.95,"balance":79280.95},{"year":13,"contributed":49000,"growth":39110.33,"balance":88110.33},{"year":14,"contributed":52000,"growth":45577.98,"balance":97577.98},{"year":15,"contributed":55000,"growth":52730.04,"balance":107730.04},{"year":16,"contributed":58000,"growth":60616,"balance":118616},{"year":17,"contributed":61000,"growth":69288.91,"balance":130288.91},{"year":18,"contributed":64000,"growth":78805.65,"balance":142805.65},{"year":19,"contributed":67000,"growth":89227.23,"balance":156227.23},{"year":20,"contributed":70000,"growth":100619.05,"balance":170619.05}]},"drivers":[{"key":"years","label":"Years to grow","step":5,"endDelta":89153.06,"sentence":"Five more years of compounding adds $89,153 to the final balance."},{"key":"monthly","label":"Monthly contribution","step":100,"endDelta":52092.67000000001,"sentence":"Each $100 more a month adds $52,093 to the final balance."},{"key":"rate","label":"Annual return","step":1,"endDelta":25904.080000000016,"sentence":"One more point of assumed return adds $25,904 to the final balance."},{"key":"principal","label":"Starting amount","step":1000,"endDelta":4038.74000000002,"sentence":"Each $1,000 more at the start adds $4,039 to the final balance."}],"sensitivity":{"byRate":[{"rate":4,"endBalance":113919.48,"growth":43919.48},{"rate":5,"endBalance":129884.82,"growth":59884.82},{"rate":6,"endBalance":148612.27,"growth":78612.27},{"rate":7,"endBalance":170619.05,"growth":100619.05},{"rate":8,"endBalance":196523.13,"growth":126523.13},{"rate":10,"endBalance":263122.95,"growth":193122.95}],"byYears":[{"years":5,"endBalance":32074.48,"contributed":25000,"growth":7074.48},{"years":10,"endBalance":63367.82,"contributed":40000,"growth":23367.82},{"years":20,"endBalance":170619.05,"contributed":70000,"growth":100619.05},{"years":30,"endBalance":386157.72,"contributed":100000,"growth":286157.72},{"years":40,"endBalance":819317.46,"contributed":130000,"growth":689317.46}]},"assumptions":[{"key":"principal","label":"Starting amount","value":10000,"unit":"usd","provided":false,"source":null},{"key":"monthly","label":"Monthly contribution","value":250,"unit":"usd-per-month","provided":false,"source":null},{"key":"rate","label":"Annual return","value":7,"unit":"percent","provided":false,"source":null},{"key":"years","label":"Years to grow","value":20,"unit":"years","provided":false,"source":null},{"key":"compounds","label":"Compounding per year","value":12,"unit":"count","provided":false,"source":null}],"sources":[],"warnings":[],"disclaimer":"This models deterministic compound growth at a rate you choose. It is not a forecast, a promised return, or investment advice. Real returns vary year to year and can be negative; taxes, fees, and inflation sit outside the model."}