Compound Interest Calculator
How much will your money grow? Add a starting amount, rate, term, and an optional monthly contribution.
Quick answer: How much will your money grow? Add a starting amount, rate, term, and an optional monthly contribution.
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Frequently asked questions
- What is compound interest?
- Compound interest is interest that earns interest. Each period, interest is added to the balance, so next period's interest is calculated on a slightly larger amount — that's what makes it grow exponentially over time.
- How do I calculate monthly compound growth?
- The monthly rate is (1 + r/n)^(n/12) − 1 where r is the annual rate and n is the number of compoundings per year. Multiply your balance by (1 + monthly rate) every month to see the growth.
- What does a monthly contribution do?
- A monthly contribution adds a fixed amount each month on top of compounding. Even small contributions add up surprisingly fast — try $100/month at 6% over 30 years and see.
- What's the difference between nominal and effective rate?
- The nominal rate is the headline annual percentage. The effective rate accounts for compounding, so a 6% nominal rate compounded monthly is an effective 6.17% per year. This calculator works with the nominal rate and lets you pick the compounding frequency.
- How much will my investment be worth after 10 years?
- Set Years to 10 and the "Final balance" line is your answer. For $10,000 at 7% with no contributions you'll see roughly $20,097 — money roughly doubles every 10 years at 7%.
- Can I include inflation?
- Not directly in this tool — it shows nominal growth. To estimate "real" growth, subtract your inflation assumption from the rate (e.g. 7% nominal − 2% inflation = 5% real).
- What is CAGR?
- CAGR (Compound Annual Growth Rate) is the constant annual rate that turns the starting balance into the final balance. It's the same number as the rate field when there are no extra contributions.
- What if interest is calculated quarterly?
- Pick "Quarterly" in the compounding dropdown. The tool converts your annual rate into the equivalent monthly rate so the math stays correct.
- Can I see a chart?
- Not yet — this version focuses on the headline numbers. The "Copy result" button lets you paste the figures into a spreadsheet to plot them.
- Can I export the results?
- Use "Copy result" to grab the final balance, interest earned and total contributions as one line of text. Paste it into a spreadsheet, email or note.