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Compound interest calculator

Project a balance from a starting amount and monthly contributions, with a clear view of deposits versus growth.

SET UP FOR YOUR COUNTRY Editable estimate

Compound interest calculator for United States

USD · 12,345.67US customary measurementsRoad distance: miles

United States planning scenario. Amounts, prices and rates are editable examples. No verified local tax bands, exemptions, benefits or lender rules are applied. Currency amounts are not exchanged.

Switch countries to open a separate scenario. Your edits are kept while this calculator is open; use Save scenario to keep them on this device.

Your details

USD
Example only. Enter the amount or rate applicable to your situation in United States.
USD
Example only. Enter the amount or rate applicable to your situation in United States.
%
Example only. Enter the amount or rate applicable to your situation in United States.
Enter years. Monthly loans and savings require a whole number of months; 0.5 years is 6 months.
Results update instantly as you change the inputs.

Projected balance

$55,290.66

Amounts in USD · United States · editable planning estimate

Total contributed$40,000.00
Projected growth$15,290.66
Years10 years
Your calculation, beautifully packaged.Download a report with this result, your inputs, the formula, and assumptions.

How this result was calculated

  1. Apply monthly growth to the current balance
  2. Add the monthly contribution at month end
  3. Growth = final balance − all contributions
  4. Country setup: United States. Displayed measurements are converted to the formula's base units internally.

Assumption: Constant nominal return compounded monthly. Real returns vary and investments can lose value; taxes and fees are excluded. United States planning scenario. Amounts, prices and rates are editable examples. No verified local tax bands, exemptions, benefits or lender rules are applied. Currency amounts are not exchanged.

Calculation version 1.0.0 · Support state: generic

Guides & conversions

Simple vs compound interest: a worked comparison
Explore the full library →

Formula and method

Each month: new balance = previous balance × (1 + annual rate ÷ 12) + contribution. Contributions are added at month end.

This calculation uses the values you enter. It runs in your browser and does not request a location or account.

Worked example

Start with 10,000, add 250 monthly for ten years and assume a 5% annual rate. The projection shows the amount contributed and the growth separately.

Questions people ask

When are contributions added?

At the end of each month after that month's growth.

Is the projection guaranteed?

No. The entered rate is an assumption for planning, not a forecast.