Compound Interest & Contribution Calculator
Explore how an opening balance and regular contributions grow under a fixed mathematical rate. Compare compounding conventions while keeping timing and exclusions visible.
Browser-based · No signup · Transparent assumptions
- 01Enter your values
- 02Adjust your settings
- 03Review your results
Enter investment details to begin
Your future value, growth chart, Rule of 72, and year-by-year breakdown will appear here.
| Frequency | Future value | Interest | Effective yield |
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| Year | Invested | Interest | Balance |
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Calculations run in this browser. A Share link contains input values in its URL; review it before sharing private financial or health information. Currency selection changes notation, not exchange rates.
When to use this calculator
Explore how a starting balance and regular savings contribute to a long-term projection. Compare monthly or yearly additions while separating the money deposited from the growth produced by an assumed mathematical rate.
Review the worked example and assumptions below, then use the supported report or copy controls to keep the result with its inputs. Calculations run in this browser; a shared URL can include the values you entered.
How to use Compound Interest & Contribution Calculator
- Enter the opening amount, annual rate and whole-year horizon.
- Choose a compounding frequency or continuous growth. Optionally add end-month or end-year contributions.
- Review invested capital, growth and the yearly table; export CSV or the calculation report.
Contribution growth uses an equivalent monthly rate
Lump-sum growth uses the selected compounding formula directly. When contributions are enabled, the simulation derives an equivalent monthly rate and adds contributions after the relevant month's interest. This is a mathematical convention, not an assertion that every deposit provider credits interest that way.
Worked example
Opening amount: 1,000; rate: 10%; annual compounding; 2 years
No contributions: 1,210
At zero rate, final balance equals opening amount plus contributions.Assumptions and limits
Returns are constant assumptions; taxes, fees, inflation and market risk are excluded. The simple-interest comparison uses the opening principal, so it is not a like-for-like contribution account. Rule of 72 is an approximation and is unavailable at zero rate.
Reference: Investor.gov compound-interest calculator. Model/source review: 19 October 2026. Results are illustrations or screening estimates; no personalized recommendation or eligibility decision is made.
Frequently asked questions
Are contributions at the start of a period?
No. This tool adds the selected monthly/yearly contribution at the end of that period.
What does continuous compounding mean?
The lump-sum calculation uses exponential growth P times exp(r times years). It is a mathematical model.
Can zero interest be modeled?
Yes. The balance is the total invested amount and no doubling time is shown.
Keep contributions distinct from the opening balance
Choose the contribution interval and review the modeled timing alongside the constant growth assumption.
Scope of this workflow
The scenario excludes market variability and the stated costs. The simple-interest comparison uses the opening principal rather than a matching contribution account.
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