Monthly Compound Interest Calculator
Interest added every month — 12 times a year. Adjust the inputs to see the year-by-year effect.
Year-by-Year Breakdown
| Year | Starting Balance | Contributions | Interest Earned | Ending Balance |
|---|---|---|---|---|
| 1 | $10,000 | $6,000 | $1,055 | $17,055 |
| 2 | $17,055 | $6,000 | $1,641 | $24,695 |
| 3 | $24,695 | $6,000 | $2,275 | $32,970 |
| 4 | $32,970 | $6,000 | $2,961 | $41,932 |
| 5 | $41,932 | $6,000 | $3,705 | $51,637 |
| 6 | $51,637 | $6,000 | $4,511 | $62,148 |
| 7 | $62,148 | $6,000 | $5,383 | $73,531 |
| 8 | $73,531 | $6,000 | $6,328 | $85,859 |
| 9 | $85,859 | $6,000 | $7,351 | $99,210 |
| 10 | $99,210 | $6,000 | $8,459 | $113,669 |
| 11 | $113,669 | $6,000 | $9,659 | $129,329 |
| 12 | $129,329 | $6,000 | $10,959 | $146,288 |
| 13 | $146,288 | $6,000 | $12,367 | $164,655 |
| 14 | $164,655 | $6,000 | $13,891 | $184,546 |
| 15 | $184,546 | $6,000 | $15,542 | $206,088 |
| 16 | $206,088 | $6,000 | $17,330 | $229,419 |
| 17 | $229,419 | $6,000 | $19,267 | $254,685 |
| 18 | $254,685 | $6,000 | $21,364 | $282,049 |
| 19 | $282,049 | $6,000 | $23,635 | $311,684 |
| 20 | $311,684 | $6,000 | $26,095 | $343,778 |
| 21 | $343,778 | $6,000 | $28,758 | $378,537 |
| 22 | $378,537 | $6,000 | $31,643 | $416,180 |
| 23 | $416,180 | $6,000 | $34,768 | $456,948 |
| 24 | $456,948 | $6,000 | $38,151 | $501,099 |
| 25 | $501,099 | $6,000 | $41,816 | $548,915 |
| 26 | $548,915 | $6,000 | $45,785 | $600,700 |
| 27 | $600,700 | $6,000 | $50,083 | $656,782 |
| 28 | $656,782 | $6,000 | $54,738 | $717,520 |
| 29 | $717,520 | $6,000 | $59,779 | $783,299 |
| 30 | $783,299 | $6,000 | $65,238 | $854,537 |
| Total | — | $190,000 | $664,537 | $854,537 |
How much does monthly compounding really change?
Monthly is the right default for planning: it matches how most people are paid and how most contributions are made. Matching the compounding cadence to the contribution cadence keeps the model honest.
The table below holds everything constant — $10,000 at 5% for 10 years, no contributions — and varies only the compounding cadence.
| Frequency | Times / year | Final balance | vs annual |
|---|---|---|---|
| Daily | 365 | $16,486.65 | +$197.70 |
| Weekly | 52 | $16,483.25 | +$194.31 |
| Monthly (this page) | 12 | $16,470.09 | +$181.15 |
| Quarterly | 4 | $16,436.19 | +$147.25 |
| Annual | 1 | $16,288.95 | — |
The spread across every cadence is $197.70 — under 1.2% of the balance. Raising the rate by a quarter of a point, or adding a small monthly contribution, moves the result far more than any change of frequency. Try it in the calculator above.
Where you meet monthly compounding
The default for most retirement projections, index-fund modelling, and any scenario where you are also contributing monthly. Mortgages and most instalment loans compound monthly too.
Other compounding frequencies
Related Calculators
Frequently Asked Questions
- Interest is calculated and added to your balance every month — 12 times a year. From the next period onward you earn interest on that interest too. The default for most retirement projections, index-fund modelling, and any scenario where you are also contributing monthly. Mortgages and most instalment loans compound monthly too.