Compound interest calculator
Project growth with compounding and regular contributions.
Compound interest calculator projects how a starting amount grows over time with compound interest, optional regular monthly contributions, and a chosen compounding frequency — showing the future value, total contributed, and total interest earned.
How to use
- Enter a starting amount, annual rate, term, compounding frequency, and an optional monthly contribution.
- Click "Calculate" to project the future value.
Common use scenarios
- Projecting how a savings or investment account might grow over time.
- Comparing the long-term impact of different contribution amounts.
- Understanding how much of future growth comes from contributions vs. interest.
- Estimating progress toward a long-term savings goal with regular contributions.
✓Content & verification reviewed: 2026-08-25
How we verify Compound interest calculator
How to confirm the projection matches the compounding assumptions you intended.
Compounding frequency changes the result meaningfully
More frequent compounding (like monthly vs. annually) produces a slightly higher future value at the same nominal annual rate, since interest starts earning interest sooner — make sure the frequency you select matches what you're actually trying to model or compare against.
Monthly contributions are added throughout, not at the end
The optional monthly contribution is factored in progressively throughout the projection period (spread according to the compounding frequency), not just added as a lump sum at the very end — this matters because contributions made earlier have more time to compound.
Total interest is future value minus total contributions
The total interest earned figure is the future value minus everything you put in (starting amount plus all contributions) — a clear way to see how much of the final total came from growth versus your own money.
Before you rely on the result
- The starting amount, rate, and term reflect what you're actually trying to project.
- The compounding frequency matches the assumption you want to model (monthly is common for savings accounts).
- The monthly contribution (if any) reflects a realistic, sustainable amount.
- You understand this assumes a constant interest rate for the entire period, which real returns rarely are.
Who this is for
- Anyone projecting how a savings or investment account might grow over time.
- People comparing the long-term impact of different monthly contribution amounts.
- Anyone wanting to understand how much of future growth comes from contributions vs. interest.
- Savers estimating progress toward a long-term goal with regular contributions.
Real-world examples
Projecting retirement savings growth
Someone contributing monthly to a retirement account projects its value in 20 years at an assumed average return, to get a rough sense of whether they're on track for their goal.
Comparing contribution amounts
Someone deciding whether to increase their monthly savings contribution projects the future value at two different contribution levels, to see the long-term difference a higher contribution makes.
Understanding growth vs. contribution split
A saver curious how much of their eventual balance will come from market growth versus their own deposits checks the total interest earned figure against their total contributions.
Limitations
- Assumes a constant interest rate and evenly spaced contributions — real returns vary.
Frequently asked questions
Does the compounding frequency really make a noticeable difference?
Yes, though usually modest — more frequent compounding (like monthly vs. annually) produces a somewhat higher future value at the same nominal rate, since interest starts compounding sooner.
Are monthly contributions added at the start or end of each period?
They're factored in progressively throughout the projection according to the compounding frequency, not added as a single lump sum at the end — earlier contributions have more time to grow.
Is this a guarantee of investment returns?
No — this assumes a constant interest rate for the entire period, which real investment returns essentially never are; treat this as a simplified planning projection, not a guarantee or prediction.
What's included in "total contributions"?
It's your starting amount plus every monthly contribution made over the full term — comparing this to the future value shows how much came from your own money versus compound growth.
🔒 Runs in your browser — nothing is uploaded. Results are for reference only; see the disclaimer. Last updated: 2026-08-25
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