See how a lump sum plus regular monthly deposits grows with compound interest – and how much of the final balance is interest you never had to save.
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With starting amount $5,000, monthly contribution $200, annual interest rate or return 6%, years 10, compounding: monthly:
Future value: $41,872.85 after 10 years
You put in $29,000.00 · interest earned $12,872.85 (31% of the balance)
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Monthly rate i = (1 + annual rate ÷ compounding periods)^(periods ÷ 12) − 1. Balance after n months = P × (1 + i)^n + M × ((1 + i)^n − 1) ÷ i, with deposits at the end of each month. Interest earned = balance − starting amount − all deposits.
Formula source: Future value of a lump sum plus end-of-month deposits, compounding converted to a monthly rate, as in the SEC Investor.gov calculator. SEC Investor.gov – compound interest calculator
Written and checked by the TanLabs Editorial Team · Last updated
Monthly compounding, deposits at the end of each month:
| $5,000 + $200/month for | At 4% | At 6% | At 8% | You deposit |
|---|---|---|---|---|
| 5 years | $19,365 | $20,698 | $22,145 | $17,000 |
| 10 years | $36,904 | $41,873 | $47,687 | $29,000 |
| 20 years | $84,468 | $108,959 | $142,438 | $53,000 |
| 30 years | $155,377 | $231,016 | $352,751 | $77,000 |
Over 30 years at 6%, $77,000 of deposits grows to about $231,000: two-thirds of the balance is interest. Time does more of the work than the rate.
Interest earned on both your deposits and on interest already earned. Over long periods the interest-on-interest part grows faster than the deposits themselves.
Very little. At 6%, daily compounding gives an effective yearly rate of about 6.18% against 6.17% for monthly. How much and how long you save matter far more.
Use the APY your savings account pays, or a cautious long-run return for investments. The SEC's investor.gov reminds savers that investment returns are not guaranteed.
Divide 72 by the yearly rate to estimate how many years it takes money to double: at 6%, about 12 years.
Yes, slightly. This calculator assumes end-of-month deposits; deposits at the start of each month earn one extra month of interest.
APY is the yearly rate after compounding. A 6% rate compounded monthly gives an APY of about 6.17%.
Sources: SEC Investor.gov – compound interest calculator