Interest CalculatorFree online financial calculator — instant results, no sign-up
Growth of savings with compound interest and regular deposits.
Estimates only, based on the inputs and assumptions shown. This is not financial, investment, tax, or legal advice. Prices, rates and local rules may change; crypto scenarios do not predict returns. Confirm important decisions with a qualified professional.
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How the result changes with starting amount
Each row below was calculated with this tool, keeping every other input at its default and changing only starting amount from half to one and a half times the default value. Use it to see how sensitive the answer is before you enter your own numbers.
| Starting amount ($) | Ending balance | Total contributions | Total interest |
|---|---|---|---|
| 5,000 | $38,331.42 | $29,000.00 | $9,331.42 |
| 7,500 | $42,403.65 | $31,500.00 | $10,903.65 |
| 10,000 (default) | $46,475.89 | $34,000.00 | $12,475.89 |
| 12,500 | $50,548.12 | $36,500.00 | $14,048.12 |
| 15,000 | $54,620.36 | $39,000.00 | $15,620.36 |
About the Interest Calculator
This calculator computes the future value of a savings balance subject to annual compound interest and recurring annual contributions. It is designed for individuals projecting long-term personal savings, retirement nest eggs, or investment milestones over a multi-year horizon.
- Starting amount
- Initial principal invested at the beginning of the period, denominated in dollars ($0 or greater).
- Annual contribution
- Amount added to the balance at the end of each year, denominated in dollars ($0 or greater).
- Interest rate
- Annual nominal interest rate as a percentage (typically between 0% and 20%).
- Years
- Total investment time horizon expressed in whole or fractional years.
Formula and method
FV = P × (1 + r)^t + C × (((1 + r)^t - 1) / r) Total Contributions = P + C × t Total Interest = FV - Total Contributions
- FVEnding balance (future value) at the end of the duration
- PStarting principal amount
- CAnnual contribution amount
- rAnnual interest rate expressed as a decimal (Interest rate / 100)
- tTime horizon in years
The tool treats annual contributions as an ordinary annuity, compounding interest once per year at the end of each period. Total contributions are calculated as the initial principal plus the sum of all yearly deposits, and total interest earned is the difference between the ending balance and total contributions.
Worked example
These are the calculator's starting values and the results it actually produces for them.
Inputs
- Starting amount10000 $
- Annual contribution2400 $
- Interest rate5 %
- Years10 years
Results
- Ending balance$46,475.89
- Total contributions$34,000.00
- Total interest$12,475.89
How to use the Interest Calculator
- 1Convert the annual interest rate from a percentage to a decimal by dividing by 100.
- 2Calculate the compound growth of the starting principal over the specified number of years.
- 3Compute the future value of the annual contributions using the ordinary annuity compounding formula.
- 4Sum the principal growth and contribution growth to determine the ending balance, then subtract total cash deposited to find total interest.
Reading your result
The ending balance represents the total projected portfolio value at the end of the term. Comparing total contributions against total interest earned highlights how much of the final value came from out-of-pocket savings versus accumulated compound growth.
Limitations
This model assumes interest compounds strictly once per year and that deposits occur at the end of each annual cycle rather than monthly. It also assumes a constant interest rate throughout the duration and does not account for income taxes, inflation, or management fees.
Common questions
Does this calculator assume deposits are made at the beginning or end of the year?+
It uses an ordinary annuity formula, meaning annual contributions are added at the end of each year and begin earning interest in subsequent years.
How does compounding frequency impact the results?+
This tool calculates annual compounding. If your account compounds monthly or daily, your actual ending balance and interest earned will be slightly higher.
Are taxes or inflation included in the total interest calculation?+
No, calculations reflect nominal returns before accounting for inflation, annual tax liabilities, or capital gains taxes.
Does the calculator save my information?+
Calculations run in your browser. While signed in, inputs and results are automatically recorded in account history; saving a result creates a separate saved record.
Further reading
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Results are estimates for informational purposes and are not financial, medical or legal advice.