Enter a starting amount, a rate, and a time horizon. Add regular contributions if you like, and see how compounding grows your money, split into principal, contributions, and interest earned.

1Starting principal
2Rate & time
% / year
years
3Additional contributionsOptional
Frequency
Max 240 (monthly × 20 years)
72,000 paid in over 20 years
Balance after 20 yearsRule of 72 · doubles every ~10.3 yrs
249,061
from 97,000 put in, 152,061 is interest · +157% total growth
Principal25,00010%
Contributions72,00029%
Interest152,06161%
Growth over time
PrincipalContributionsInterest
249k
187k
125k
62k
0
now4y8y12y16y20y
Around year 15, accumulated interest overtakes everything you have put in. From then on, your money is mostly earning rather than being added.
Year-by-year breakdown

How the balance builds, one year at a time.

Each row shows the running total at year-end: what you have contributed, the interest earned so far, and the resulting balance. Watch the interest column accelerate as it starts compounding on itself.

YearContributedInterestBalanceComposition
128,6001,86630,466
232,2004,11436,314
335,8006,77142,571
439,4009,86749,267
543,00013,43156,431
646,60017,49664,096
750,20022,09972,299
853,80027,27581,075
957,40033,06690,466
1061,00039,514100,514
1164,60046,665111,265
1268,20054,569122,769
1371,80063,279135,079
1475,40072,850148,250
1579,00083,343162,343
1682,60094,822177,422
1786,200107,357193,557
1889,800121,022210,822
1993,400135,895229,295
2097,000152,061249,061
This calculator compounds interest annually on the running balance. Contributions are made at the end of each chosen period and earn simple interest for the remainder of that year. Results assume a constant annual rate and are illustrative. Not financial advice.
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