Compound Interest Calculator
Project how savings grow over time with regular monthly contributions.
Wealth Breakdown
| Year | Contributions | Interest | Total Balance |
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Compound interest is what makes long-term saving powerful: each period you earn interest not just on your original money but on the interest already added. This calculator projects the growth of a starting balance combined with a regular monthly contribution, and breaks the result into how much you put in versus how much came from growth. It also shows a year-by-year table so you can watch the balance build. Everything runs in your browser, and nothing you enter is stored.
How the projection works
The calculator steps through the term one month at a time, adding your monthly contribution as it goes. Each month it applies a share of compound growth sized to the compounding frequency you choose — daily, monthly, quarterly, or annually — so that a full year's worth of steps reproduces the standard compound-growth relationship:
A = P × (1 + r ÷ n)^(n × t) (plus each month's contribution, compounded)
Here n is how many times a year interest compounds. As an example, starting with $1,000, adding $100 a month for 10 years at a 7% annual rate compounded monthly grows to roughly $19,300. Of that, about $13,000 is money you contributed and around $6,300 is interest — the gap widens the longer you leave it invested, and more frequent compounding nudges the total up slightly.
Reading the results honestly
The split between contributions and interest is the useful part: early on most of the balance is your own money, but given enough time the interest portion can overtake it. Remember the projection assumes a single, steady rate of return that never changes. Real investments fluctuate, inflation erodes the future value of the total, and returns are rarely constant year to year. Use the figure as a rough trajectory for comparing scenarios, not a promise of a specific balance.
Frequently Asked Questions
Are contributions added monthly?
Yes. The projection adds your contribution once a month, while interest compounds at whatever frequency you select — daily, monthly, quarterly, or annually — which mirrors how many regular savings and investment plans work.
Does the compounding frequency change the result?
A little. More frequent compounding — daily rather than annually, say — earns interest on interest sooner, so the final balance is slightly higher for the same rate. The effect is modest but real, and the frequency selector lets you compare it.
Why is the interest portion small at first?
Compounding needs time. In the early years the balance is mostly the money you have paid in; the share coming from interest grows as the balance — and the interest earned on it — gets larger.
Is this a guaranteed forecast of my returns?
No. It assumes a fixed annual rate, but real returns vary and inflation reduces future buying power. This is a planning estimate for information only, not financial advice.
Do you save the numbers I enter?
No. The calculation runs entirely in your browser and nothing is uploaded or stored.