Compound interest calculator
Estimate future value and total interest for savings or investments using compound interest.
What is a compound interest calculator?
A compound interest calculator estimates how your money can grow over time when interest is added to your balance and future interest is earned on that new balance. It’s useful for savings goals, investment planning, and comparing different rates or compounding frequencies.
What is compound interest?
Compound interest means you earn interest on your original principal and on the interest you’ve already earned. This “interest on interest” effect is why compounding is powerful over long periods. The more frequently interest compounds (monthly vs yearly), the faster the balance can grow, assuming the same annual rate.
How to calculate compound interest online
For a one-time deposit, the standard formula is: A = P × (1 + r/n)^(n×t). Here, P is principal, r is annual rate as a decimal (8% → 0.08), n is compounding frequency per year, and t is time in years. This calculator also supports optional contributions each period (for example, adding a fixed amount every month).
Step-by-step (how to use this calculator)
1) Enter principal: your starting amount.
2) Enter annual rate: the yearly interest rate in %.
3) Choose time: number of years you’ll keep the money invested.
4) Choose compounding: yearly/quarterly/monthly/daily.
5) Optional contributions: if you add money each period, enter that amount.
Compound interest calculation formula
Final amount: A = P × (1 + r/n)^(n×t)
Total interest: A − P (ignoring contributions)
Example compound interest calculation
Example: ₹10,000 at 8% for 10 years (monthly compounding) → use the calculator to get the ending balance and total interest. Add monthly contributions (optional) to model regular investing.
Compounding frequency: does it matter?
Yes, but usually the difference is small for typical rates. Monthly compounding can produce a slightly higher ending balance than yearly compounding because interest is added to the base more often. Over long time periods, even small differences can add up.
Rule of 72 (quick estimate)
A popular shortcut is the Rule of 72: approximate years to double ≈ 72 ÷ (annual rate in %). For example, at 8% it’s roughly 9 years. It’s an estimate, but useful for quick mental checks.
When should you use this tool?
Use it when planning savings targets, comparing investment options, estimating future value, or understanding how rate changes and contributions affect long-term growth.
Why use this online compound interest calculator?
It helps you compare scenarios quickly: different rates, different time horizons, and different compounding frequencies. It’s useful for planning savings goals, evaluating investment growth assumptions, and understanding how long-term compounding changes outcomes even with small rate differences.
FAQs
Does compounding daily always help? It can increase returns slightly versus monthly/yearly at the same annual rate.
How do contributions affect growth? Regular contributions increase invested amount and can significantly increase ending balance.
Is this exact? It’s an estimate based on constant rate and fixed compounding; real products may have fees and varying rates.