Compound Interest Calculator
Project a future balance from an initial investment, monthly contributions and an assumed interest rate. Compare compounding frequencies and separate your deposits from interest earned.
Future savings
Nominal annual rate with the selected compounding frequency. Contributions occur at the selected monthly timing. Years are rounded to full months. Tax, inflation, fees and variable market returns are excluded. Comparison rates are illustrative, not forecasts.
See your savings over time
These are hypothetical constant-rate scenarios. Returns, taxes, fees and inflation can change the outcome.
| Year | Contributions | Balance | Interest |
|---|---|---|---|
| 0 | $10,000.00 | $10,000.00 | $0.00 |
| 1 | $12,400.00 | $12,967.39 | $567.39 |
| 2 | $14,800.00 | $16,086.60 | $1,286.60 |
| 3 | $17,200.00 | $19,365.39 | $2,165.39 |
| 4 | $19,600.00 | $22,811.93 | $3,211.93 |
| 5 | $22,000.00 | $26,434.80 | $4,434.80 |
| 6 | $24,400.00 | $30,243.03 | $5,843.03 |
| 7 | $26,800.00 | $34,246.09 | $7,446.09 |
| 8 | $29,200.00 | $38,453.96 | $9,253.96 |
| 9 | $31,600.00 | $42,877.11 | $11,277.11 |
| 10 | $34,000.00 | $47,526.55 | $13,526.55 |
What if the rate changes?
| Nominal annual rate | Future balance |
|---|---|
| 3% | $41,441.82 |
| 5% | $47,526.55 |
| 7% | $54,713.58 |
Formula checked · NumberSwift · Review process
For informational purposes only. Results are estimates and do not constitute financial advice.
How this calculator works
The nominal annual rate and compounding frequency determine an effective monthly growth rate. Initial savings grow for the whole horizon. Monthly deposits grow from the selected start or end of each month. The timeline separates deposited capital from interest, while alternative rates illustrate sensitivity rather than forecasting market returns.
Formula
Monthly growth r = (1 + annual rate / 100 / m)^(m/12) − 1, with m compounding periods per year. Future value = P(1+r)^n + C((1+r)^n − 1)/r, where P is initial savings, C the monthly contribution and n the months. For start-of-month deposits, multiply the contribution term by (1+r). At 0%: P + Cn.
Assumptions & limitations
Nominal annual rate with the selected compounding frequency. Contributions occur at the selected monthly timing. Years are rounded to full months. Tax, inflation, fees and variable market returns are excluded. Comparison rates are illustrative, not forecasts.
Sources & reference material
- OpenStax: annuities ↗
Background for fixed periodic payments and contributions.
- Investor.gov: compound interest calculator ↗
Reference for principal, contributions, rate and compounding inputs; not a return forecast.
Worked example
Start with $10,000, add $300 at each month end and assume a 6% nominal annual rate compounded monthly for 10 years. The monthly rate is 0.5% over 120 months. You contribute $46,000 in total; the model projects $67,357.77, including $21,357.77 interest. This is a constant-rate illustration, not a return forecast.
If you know the future balance you want instead of the monthly deposit, use the Savings Goal Calculator to solve for the contribution.
Our approach to calculations ↗Common questions
What is a nominal annual rate?
It is the annual rate before compounding. The selected frequency determines the equivalent monthly growth factor used for contributions.
Do beginning-of-month deposits earn more?
At a positive rate, yes. They receive one extra month of growth compared with otherwise identical end-of-month deposits.
Are the lower and higher rate lines forecasts?
No. They are illustrative scenarios two percentage points below and above the entered rate, with the lower rate bounded at zero.