Compound interest guide
How to Use This Compound Interest Calculator
A step-by-step guide to each input, the chart, the annual table, sharing URLs, and common mistakes to avoid.
Try this scenario
Open the calculator with this guide's example already filled in, then adjust the monthly contribution, return, or timeline to compare your own scenario.
Open calculator exampleKey Takeaways
- Each input controls a specific part of the growth model.
- The chart separates money invested from interest earned.
- Shareable URLs make it easy to save or compare scenarios.
Example Scenarios
| Scenario | Principal | Monthly | Return | Years | Result |
|---|---|---|---|---|---|
| Default example | $100,000 | $5,000 | 5% | 10 | About $928,272 final balance |
| Lower contribution test | $100,000 | $2,500 | 5% | 10 | About $541,120 final balance |
Step 1: Enter the starting principal
Principal is the amount already available at the start of the calculation. If you are starting from zero, set this to 0. If you already have money invested or saved, enter that balance.
The principal compounds for the full period, so it can have a large effect on the final result.
Step 2: Add monthly contribution
Monthly contribution is the amount you plan to add each month. This is often the most controllable input because it comes from your saving rate.
Try several contribution levels. The result cards make it easy to see how much of the future balance comes from deposits and how much comes from interest.
Step 3: Choose return, years, and frequency
Annual interest rate is the expected yearly return. For planning, use a range rather than one perfect number. Years is the time horizon. Compounding frequency controls whether growth is applied monthly or yearly.
Monthly compounding usually produces a slightly higher result than yearly compounding. The difference grows with time, but the contribution rate, return rate, and timeline usually matter more.
Step 4: Read the chart and table
The chart compares total balance with total invested. The space between them is interest earned. The annual table gives a year-by-year breakdown, which is useful for checking whether a goal is on track.
Use the share button after setting up a scenario. It copies a URL with the inputs encoded, so you can return to the same calculation later or send it to someone else.
Questions
Are calculations saved on the server?
No. The calculator runs in your browser. Shared links store inputs in the URL, not in a user account.
Is this financial advice?
No. The calculator is for education and scenario planning. It does not recommend investments or predict future returns.