Compound Interest Calculator
This calculator shows how your savings grow when interest earns interest over time. Enter your starting balance, the APY you earn, your compounding frequency, and any regular deposits. The tool uses the standard compound interest formula to project your future balance, so you can compare daily, monthly, and yearly compounding side by side.
Balance after years
of your own money, plus of interest.
- Starting amount
- Deposits over the term
- Interest earned
- Final balance
Assumes the rate you entered holds for the whole term and nothing is withdrawn. Interest on a taxable account is generally taxable income. A calculation, not financial advice.
Effective annual rate
Interest, year 1
Interest, final year
Interest share of balance
Year-by-year build-up
| Year | Opening | Deposits | Interest | Closing |
|---|
Swipe the table sideways to see every column.
How the Formula Works
Compound interest means you earn interest on your original deposit plus all the interest already added. The formula is FV = P(1 + r/n)^(nt), where P is your principal, r is the annual rate as a decimal, n is how many times interest compounds per year, and t is time in years. If you start with $5,000 and earn an illustrative 4.5% annual rate compounded monthly, n equals 12. After one year, your balance reaches roughly $5,230 in interest from a single deposit with no extra contributions. Add $200 per month, and each deposit starts earning its own interest immediately. After 15 years of monthly $200 contributions at that same illustrative rate, your total balance grows to approximately $61,100 even though you only deposited $41,000 out of pocket. The remaining $20,100 came from compounding alone. The calculator handles this math instantly for any combination of inputs you choose.Daily, Monthly, or Yearly Compounding
Compounding frequency determines how often earned interest gets added to your balance and starts earning its own interest. Daily compounding adds interest every day. Monthly adds it once a month. Yearly adds it once at the end of each year. For most savings balances, the difference is small but real. Take $5,000 at an illustrative 4.5% annual rate for 10 years with no additional deposits. Compounded yearly, you end with roughly $7,765. Compounded daily, you end with roughly $7,841. The gap is about $76 meaningful but not dramatic. The difference grows with larger balances. On $100,000 over 10 years at the same illustrative rate, daily compounding produces roughly $1,500 more than yearly compounding. Banks and credit unions typically compound savings daily and credit monthly. When comparing accounts, focus on the APY rather than the stated rate. APY already accounts for compounding frequency, making apples-to-apples comparison straightforward.Projections assume a fixed rate for the full period. Actual savings rates change over time, so treat results as planning estimates rather than guarantees.
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Sources
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Formula: FV = P(1 + r/n)^(nt), standard compound interest formula.
- Annual percentage yield formula — Truth in Savings Act, Regulation DD, 12 CFR Part 1030, Appendix A (Consumer Financial Protection Bureau).
- Compound interest and annuity formulas — standard financial mathematics; every figure is computed from the inputs you enter.