📈 Compound Interest Calculator
Estimate how an initial investment and regular monthly contributions may grow with compound interest. View balances, contributions, and earnings in USD or CAD.
Financial disclaimer: This compound interest calculator is an educational estimate, not financial, tax or investment advice. Results assume a constant nominal annual rate and regular monthly deposits. Actual balances may differ due to variable rates, posting schedules, fees, taxes or market performance. Returns are not guaranteed.
How to use this compound interest calculator
- Choose 🇺🇸 US (USD) or 🇨🇦 CA (CAD). Enter your initial principal, using 0 if you are starting with monthly deposits only. The region changes currency labels without converting your amounts.
- Add an optional monthly contribution and enter a nominal annual interest rate as a percentage: enter 6 for 6%. Leave the contribution blank for no recurring deposits; do not enter APY as the nominal rate.
- Set the term using whole years and optional additional months from 0 to 11. The total must be between 1 month and 100 years; use 0 years for a term shorter than one year.
- In Advanced Options, choose annual, semiannual, quarterly, monthly or daily compounding. Monthly (12 times per year) and end-of-month deposits are the defaults; beginning-of-month deposits grow for one extra month each.
- Select Calculate growth to view the estimated balance, contributions, interest and effective rates. Review the yearly breakdown or expand the monthly table to inspect individual months.
Compound interest formula
Let P be the initial principal, M the fixed monthly contribution, R the nominal annual rate as a decimal (6% = 0.06), and m the number of compounding periods per year. The total number of months is n = 12 × full years + additional months. The equivalent monthly rate i is:
The nominal annual rate is the input before compounding. The effective annual rate is (1 + R / m)^m − 1, while i is the equivalent monthly rate and (1 + i) is the monthly growth factor. For monthly compounding, m = 12 and i = R / 12.
For a positive rate and deposits at each month's end, the first term below is the future value of the principal. The second term is the future value of all monthly contributions:
For beginning-of-month deposits, multiply only the contribution term by (1 + i). At 0% interest, FV = P + M × n for either timing. Total contributions equal P + M × n; estimated interest equals FV minus total contributions. Intermediate amounts are not rounded to cents.
Every frequency uses equivalent monthly growth for regular monthly deposits. Daily compounding uses a fixed 365-day model year, without simulating actual calendar days, daily bank balances or interest posting dates.
When is a compound interest calculator useful?
Use this investment growth calculator to explore long-term savings, regular monthly investing or growth from a lump sum. A compound interest calculator with monthly contributions helps separate your own deposits from the growth produced by an assumed constant rate.
To use it as a monthly compound interest calculator, keep compounding set to Monthly. For a daily compound interest calculator estimate, select Daily in Advanced Options. Compare one setting at a time while keeping the nominal annual rate, term, deposits and deposit timing unchanged. These are mathematical scenarios, not predictions of market returns or comparisons of bank products.
For example, an initial $10,000 plus $200 deposited at each month-end, at a 6% nominal annual rate compounded monthly for 10 years, produces an estimated $50,969.84: $34,000 contributed and $16,969.84 in modeled interest. Changing only the deposits to month-beginning produces $51,133.72. These amounts use the selected currency: USD for US or CAD for CA, with no currency conversion.
Compound interest calculator FAQ
How does compound interest work?
Compound interest earns growth on your initial principal and on interest already accumulated. This model applies a constant nominal annual rate and the selected compounding frequency. With monthly deposits, each contribution also grows for the time it remains invested.
How do monthly contributions affect growth?
Compound interest with deposits combines your starting balance with a fixed amount added every month. Contributions increase the money invested, and earlier deposits have more time to earn growth at a positive rate. Leave the monthly contribution blank to calculate growth from the initial investment alone.
Is daily compounding better than monthly?
At the same positive nominal annual rate, daily compounding produces a slightly higher effective annual rate than monthly compounding. Choose Daily or Monthly in Advanced Options to compare estimates, keeping other inputs unchanged. Daily uses 365 periods per model year and equivalent monthly growth for deposits; it does not reproduce actual bank posting dates or guarantee a better investment.
What is the difference between APR and APY?
APY includes the effect of compounding over a year. APR is commonly used for annualized borrowing costs and can include certain fees. This calculator requires a nominal annual interest rate, not an APY or a fee-inclusive loan APR, and reports an effective annual rate for the chosen frequency. Entering APY as the nominal rate can overstate growth.
Are monthly contributions added at the beginning or end of the month?
The default is the end of each month, after that month's growth. In Advanced Options, choose Beginning of month to add each deposit before that month's growth. There are exactly as many deposits as months in the term; at a positive rate, beginning-of-month deposits have one extra month of growth each.
Can I start with no money and add something each month?
Yes. Enter 0 for the initial investment and a positive monthly contribution. To calculate without recurring deposits, enter a positive initial investment and leave the contribution blank. The two amounts cannot both be zero, and the term must be at least one month.
Does this estimate include taxes, fees, or inflation?
No. It assumes a fixed nominal annual rate and equal monthly deposits, with no withdrawals, taxes, fees, or inflation adjustment. It does not model changing investment returns or account-specific rules. The estimate is not a guaranteed return or personalized investment advice.
Can I calculate compound interest in Canada?
Yes. Choose CA to display amounts in CAD, or US for USD. This compound interest calculator for Canada uses the same mathematics as the US setting: switching regions does not convert currencies or change the assumed rate. Canadian taxes, account rules, and actual interest posting schedules are not modeled.