Compound Interest Calculator

See how your money grows over time with compound returns. Adjust the rate, contribution, and time period to compare scenarios.

Investment Details
$
$
$6,000 / year
%
S&P 500 historical avg: ~10%
years
Quick Scenarios
Future Value
$548,914.96
after 25 years at 8% · 3.4x your money
Total Balance
$549k
Total Contributed
$160k
Interest Earned
$389k
70.9% of balance
Growth Multiple
3.4x
Money Sources
Initial Deposit$10,000 (1.8%)
Contributions$150,000 (27.3%)
Interest Earned$388,915 (70.9%)
Year-by-Year Growth
YearContributedInterestBalance
Year 1$16,000$1,055$17,055
Year 2$22,000$2,695$24,695
Year 3$28,000$4,970$32,970
Year 4$34,000$7,932$41,932
Year 5$40,000$11,637$51,637
Year 6$46,000$16,148$62,148
Year 7$52,000$21,531$73,531
Year 8$58,000$27,859$85,859
Year 9$64,000$35,210$99,210
Year 10$70,000$43,669$113,669
Year 11$76,000$53,329$129,329
Year 12$82,000$64,288$146,288
Year 13$88,000$76,655$164,655
Year 14$94,000$90,546$184,546
Year 15$100,000$106,088$206,088
Year 16$106,000$123,419$229,419
Year 17$112,000$142,685$254,685
Year 18$118,000$164,049$282,049
Year 19$124,000$187,684$311,684
Year 20$130,000$213,778$343,778
Year 21$136,000$242,537$378,537
Year 22$142,000$274,180$416,180
Year 23$148,000$308,948$456,948
Year 24$154,000$347,099$501,099
Year 25$160,000$388,915$548,915

Frequently Asked Questions

What is compound interest?

Compound interest is interest earned on both your initial investment and previously earned interest. Over time, this creates exponential growth — your money earns returns on its returns. The longer you invest, the more powerful the compounding effect becomes.

How does compounding frequency affect returns?

More frequent compounding (monthly vs. annually) means interest is calculated and added to your balance more often, so each subsequent calculation uses a slightly higher balance. Monthly compounding will yield more than annual compounding at the same rate, though the difference is modest.

What return rate should I use?

The S&P 500 has historically returned about 10% annually before inflation (~7% after inflation). A balanced portfolio might return 7%. Conservative bond-heavy portfolios might return 4-5%. Use the Quick Scenarios buttons to compare different rates instantly.

How much should I invest per month?

Even small monthly contributions make a big difference over long periods. $200/month at 8% over 30 years grows to nearly $300,000. The key is starting early and being consistent — time in the market matters more than timing the market.

Building a rental portfolio? RentalSlate helps independent landlords manage tenants, leases, finances, and tax reports — free.

Try RentalSlate Free