Compound Interest Calculator
Calculate how your savings or investment grows over time with compound interest — free and instant.
Deposit frequency stays separate from interest compounding.
Advanced options
Your result
Updates as you type- Final amount
- $16,470
- Interest earned
- $6,470
- Total contributions
- $0
Your balance after 10 years.
Growth on top of your deposit and contributions.
Deposits added beyond your starting balance.
Yearly growth schedule
| Year | Contributions | Interest earned | Ending balance |
|---|---|---|---|
| 1 | $0 | $512 | $10,512 |
| 2 | $0 | $538 | $11,049 |
| 3 | $0 | $565 | $11,615 |
| 4 | $0 | $594 | $12,209 |
| 5 | $0 | $625 | $12,834 |
| 6 | $0 | $657 | $13,490 |
| 7 | $0 | $690 | $14,180 |
| 8 | $0 | $725 | $14,906 |
| 9 | $0 | $763 | $15,668 |
| 10 | $0 | $802 | $16,470 |
Informational only — not financial advice. This is a simplified model that excludes fees, taxes and your personal circumstances. Read the full disclaimer.
Balance Breakdown
- Starting amount
- 61%
- Interest earned
- 39%
Balance over time
Method, assumptions, and tips
Contribution frequency is independent of interest compounding. Intermediate deposit periods use the equivalent fractional-period rate, with no fees, tax, inflation or changing returns.
Assumes a fixed annual interest rate for the whole period.
No withdrawals; regular contributions are optional and modeled if you enter one.
Interest compounds at the selected frequency (e.g. monthly).
Interest is calculated on your growing balance, not just your starting amount — so the more often it compounds, the faster your money grows.
Compounding frequency matters less than time — doubling the years moves the final number far more than switching monthly to daily.
Comparing savings accounts or projecting a lump sum you plan to leave untouched.
How it works
How compound interest actually works
A compound interest calculator with monthly compounding shows what happens when interest is added to your balance and then earns interest itself. That second-order effect is the whole difference between compound and simple interest, and over long periods it dominates.
The final amount A comes from the principal P, the annual rate r, the number of compounding periods per year n, and the number of years t:
A = P × (1 + r/n)^(n×t)
With simple interest you would earn the same amount every year forever. With compounding, each year starts from a larger balance than the last, so each year earns more than the one before.
Frequency matters less than people expect
Compounding frequency is the input people fixate on, and it is the one that moves the answer least. Here is $10,000 at 5% for 10 years:
| Compounding | Final amount | Interest earned |
|---|---|---|
| Annually | $16,289 | $6,289 |
| Quarterly | $16,436 | $6,436 |
| Monthly | $16,470 | $6,470 |
| Daily | $16,487 | $6,487 |
The gap between annual and daily compounding is about $198 over a decade — roughly 3% of the interest earned. Meaningful, but small.
Time and rate are the real levers
Double the term instead and the same $10,000 at 5% compounded monthly reaches about $27,126 after 20 years — the second decade earns nearly $1.7 for every $1 the first decade earned. That asymmetry is why starting earlier beats optimising the product.
What this calculator assumes
- A fixed rate for the whole period. Real savings rates move; real investment returns move a great deal more.
- No withdrawals. Regular contributions are supported (optional) and grow the final figure substantially; the calculator has no way to model taking money out partway through.
- No tax. Interest is often taxable, which reduces the real return.
- No inflation adjustment. The final figure is in future dollars, which will buy less than today's.
That last point is worth sitting with. If inflation runs at 3% while you earn 5%, your real return is closer to 2%. The balance grows; the purchasing power grows far more slowly.
Reading the result honestly
- For a savings account, the rate is usually reliable but variable, and the bank can change it.
- For an investment, any single rate is an assumption, not a promise. Returns vary year to year and can be negative. Model a pessimistic case as well as an optimistic one.
- Compare products on the effective annual rate, which already folds compounding frequency in, rather than comparing headline rates with different frequencies.
Everything is computed in your browser as you type, so you can model real balances without sending them anywhere.
Reference and model boundaries
Investor.gov’s compound-interest calculator, from the U.S. Securities and Exchange Commission, provides an independent savings-scenario reference. Match initial balance, rate, term and compounding frequency before comparing outputs. Our optional deposits use separately selected timing and frequency; bank posting rules can differ. Neither a fixed-rate model nor a matching example establishes an investment’s future return.
FAQ
Are contribution frequency and compounding independent?
Yes. Select monthly, quarterly or annual deposits independently of interest compounding. Beginning-of-period deposits earn interest for that period; end-of-period deposits do not. Between compounding dates the model uses an equivalent fractional-period rate, so actual bank posting rules can differ.
How is compound interest calculated?
With the formula A = P × (1 + r/n)^(n×t), where P is your starting amount, r is the annual rate, n is how many times per year interest compounds, and t is the number of years. Each period earns interest on the previous balance, including previously earned interest.
What compounding frequency should I use?
Whatever your bank or investment states — savings accounts are often daily or monthly, some bonds and investments are annual. It matters less than people expect: on $10,000 at 5% over 10 years, daily compounding beats annual by about $198.
Does this include regular deposits?
Yes, optionally. Enter a Regular contribution and choose its separate Contribution frequency, such as monthly. Advanced options choose beginning or end timing. On $10,000 at 5% compounded monthly over 10 years, adding $100 a month grows the final amount from about $16,470 to about $31,998. Leave it at zero to model the starting amount alone.
Does the result account for tax or inflation?
Neither. Interest is often taxable, and the final figure is in future dollars. If inflation runs at 3% while you earn 5%, your real return is closer to 2% in purchasing power.
Why does the second half of the term earn so much more?
Because each year starts from a larger balance. Growth is exponential rather than linear, so the later years compound on a much bigger number. This is why starting earlier usually matters more than finding a slightly better rate.
Is this reliable for investment returns?
Treat it as a model, not a forecast. It assumes one fixed rate for the whole period, whereas real investment returns vary year to year and can be negative. Run a pessimistic scenario alongside your optimistic one.