1. Pick a principal
Start with a principal — the amount you have today.
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Compound interest calculator
Project savings growth over time.
Final balance
$170,619.05
Total interest
$100,619.05
Contributions
$60,000.00
| Year | Start | Interest | Contrib. | End |
|---|---|---|---|---|
| 1 | $10,000.00 | $821.05 | $3,000.00 | $13,821.05 |
| 2 | $13,821.05 | $1,097.27 | $3,000.00 | $17,918.32 |
| 3 | $17,918.32 | $1,393.46 | $3,000.00 | $22,311.78 |
| 4 | $22,311.78 | $1,711.07 | $3,000.00 | $27,022.85 |
| 5 | $27,022.85 | $2,051.63 | $3,000.00 | $32,074.48 |
| 6 | $32,074.48 | $2,416.81 | $3,000.00 | $37,491.29 |
| 7 | $37,491.29 | $2,808.39 | $3,000.00 | $43,299.69 |
| 8 | $43,299.69 | $3,228.28 | $3,000.00 | $49,527.97 |
| 9 | $49,527.97 | $3,678.53 | $3,000.00 | $56,206.50 |
| 10 | $56,206.50 | $4,161.32 | $3,000.00 | $63,367.82 |
| 11 | $63,367.82 | $4,679.01 | $3,000.00 | $71,046.83 |
| 12 | $71,046.83 | $5,234.13 | $3,000.00 | $79,280.95 |
| 13 | $79,280.95 | $5,829.37 | $3,000.00 | $88,110.33 |
| 14 | $88,110.33 | $6,467.65 | $3,000.00 | $97,577.98 |
| 15 | $97,577.98 | $7,152.07 | $3,000.00 | $107,730.04 |
| 16 | $107,730.04 | $7,885.96 | $3,000.00 | $118,616.00 |
| 17 | $118,616.00 | $8,672.91 | $3,000.00 | $130,288.91 |
| 18 | $130,288.91 | $9,516.74 | $3,000.00 | $142,805.65 |
| 19 | $142,805.65 | $10,421.58 | $3,000.00 | $156,227.23 |
| 20 | $156,227.23 | $11,391.83 | $3,000.00 | $170,619.05 |
The projection is computed in this browser tab. Nothing is uploaded.
How it works
2. Set rate + term
Add a yearly interest rate, time horizon, and how often interest compounds. Add a monthly contribution if you'll keep depositing.
3. See the growth
Read the final balance, total interest, and a year-by-year breakdown. Everything is local.
About the Compound Interest Calculator tool
The Compound Interest Calculator projects how a savings or investment balance grows over time when interest is earned on interest. Start with a principal, add an annual interest rate and a time horizon, choose how often interest compounds (from daily to annually), and optionally include a regular monthly contribution. The tool returns the final balance, the total interest earned, and a year-by-year breakdown so you can watch the compounding curve steepen as the balance grows.
It is a clear way to model a savings goal, compare what a higher rate or an extra monthly deposit does to the end result, or understand the difference between APR and APY. Monthly contributions are added across each compounding period, after that period's interest, mirroring how most accounts actually work. The whole projection runs in your browser — your figures never leave the page — and the calculator is free, needs no account, and works offline once the page has loaded.
Frequently asked questions
What is compound interest?
Compound interest means each period's interest is added to the balance, so the next period earns interest on a slightly larger amount. Over time this compounding accelerates growth — "interest on interest".
Does compounding frequency matter much?
Daily compounding gives slightly more growth than monthly, which gives more than annually — but the differences are smaller than the rate or time horizon. Many savings products advertise APR vs APY, where APY is the rate after compounding.
How are monthly contributions handled?
Contributions are split into the compounding cadence (e.g. a $300/mo deposit becomes $3,600/yr split evenly across compounding periods). Each period the contribution is added at the end, after that period's interest.
Is anything sent to a server?
No. The inputs and the projection never leave the browser.