Compound Interest on a Single Deposit
Estimate the future balance and interest using a rate and compounding schedule you choose.
Compound Interest Calculator
Table of Contents
Formula and inputs
The calculator uses A = P(1 + r/n)^(nt) and I = A − P. A is the final amount and I is interest earned, both in dollars. P is the initial deposit in dollars; r is the annual rate as a decimal (enter 5 for 5%, then r = 0.05); n is compounding periods per year (12 means monthly); and t is time in years. The same currency unit applies to P, A, and I.
Interest is credited to the balance each period. The calculator accepts a nonnegative principal, rate from 0% to 100%, nonnegative years, and a positive compounding frequency. It displays dollars rounded to cents.
Worked example: $10,000 at 5% for five years
Enter $10,000 initial investment, 5% annual interest, 5 years, and 12 compounding periods per year. Then A = $10,000 × (1 + 0.05/12)^(12 × 5) = $12,833.59. Interest earned is $12,833.59 − $10,000 = $2,833.59. These are the two amounts shown by the calculator after rounding to cents.
What changes the result
A larger starting deposit scales the dollar result. A higher entered rate, longer time, or more frequent compounding increases the mathematical result when the other inputs stay fixed. This comparison assumes the stated annual rate does not change.
When this estimate is useful
Use it to compare fixed-rate scenarios for one deposit or to check the arithmetic in a quoted compounding example. To compare actual accounts or loans, check their rate definitions, payment schedules, and terms: a loan with repayments or an investment with ongoing contributions needs a cash-flow calculation.
Assumptions and limits
The entered rate is your assumption, not a prediction. The result holds it constant and excludes contributions, withdrawals, taxes, fees, inflation, and changes in interest rate. It also assumes each period earns exactly r/n; a provider may use a different day-count rule or crediting schedule. The result is for information only and is not financial or legal advice.
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Sources and review date
Frequently Asked Questions
Does this result include regular deposits or withdrawals?
No. The calculation compounds only the initial deposit. There is no input for later deposits or withdrawals, so add them separately when planning cash flows.
Is the annual rate an actual or guaranteed return?
No. The rate is the percentage you enter for a hypothetical fixed-rate calculation. It is not a market forecast or a guarantee of an account or investment return.
Why does monthly compounding differ from annual compounding?
At the same stated annual rate, monthly compounding credits interest 12 times per year, so each later month can earn interest on earlier credits. Enter 12 for monthly or 1 for annual compounding.