Compound Interest Calculator
Estimate how your money grows over time with compound interest and regular contributions.
Compounding Frequency
Example Scenarios
- $10,000 at 7% for 10 years
- $5,000 + $250/month at 6%
- $20,000 + $100/month at 8%
Functions & Usage
This compound interest calculator estimates how money grows over time based on starting balance, annual rate, compounding frequency, and monthly contributions.
Key Features
- Calculates estimated future value
- Includes monthly contribution support
- Supports monthly, quarterly, and annual compounding
- Shows total contributions and estimated interest earned
How to use the compound interest calculator
Enter your starting amount — the money you have to invest today — in the Starting Amount field. Set your expected annual interest rate, how many years you will keep the money invested, and your monthly contribution (enter 0 if you are not adding money regularly). Finally, choose your compounding frequency: monthly is the most common for savings accounts and index funds, quarterly for some bonds and CDs, annually for simpler estimates. The Estimated Future Value updates instantly as you change any input. Click any Example Scenario to load a preset and see how different starting conditions compare.
How compound interest works
Compound interest means you earn interest on your interest, not just on your original deposit. Each compounding period, the interest earned is added to your balance, and the next period's interest is calculated on the larger total. The formula for a lump sum is: FV = P × (1 + r/n)^(n×t), where P is the principal, r is the annual rate, n is the number of compounding periods per year, and t is the time in years. With regular contributions added each period, the future value grows even faster. The difference between compound and simple interest becomes dramatic over long time horizons: $10,000 at 7% simple interest for 30 years grows to $31,000, while at 7% compound interest it grows to over $76,000.
When to use this calculator
Use this calculator when planning long-term savings and investments. It is ideal for retirement planning — see how much your 401(k) or IRA contributions could grow over 20 or 30 years at a projected market return. College savers can estimate a 529 plan balance by the time a child reaches 18. Anyone opening a high-yield savings account can model how much a one-time deposit plus monthly top-ups will be worth in 5 or 10 years. Investors comparing CD rates can change the compounding frequency from monthly to annually to see the real difference. The calculator also helps illustrate why starting early matters: an extra 5 years at the beginning of a compounding timeline often outweighs doubling the monthly contribution later.
Frequently asked questions
What is the difference between monthly and annual compounding?
Monthly compounding applies interest 12 times per year, each time on the slightly larger balance. Annual compounding applies interest once. Monthly compounding produces a higher final value for the same annual rate. For example, $10,000 at 6% compounded monthly for 10 years grows to ~$18,194 vs. ~$17,908 with annual compounding — a meaningful difference over longer periods.
Does the monthly contribution field assume contributions at the start or end of each period?
The calculator adds contributions at the end of each compounding period (ordinary annuity), which is the standard assumption for most retirement and savings accounts where money is deposited at the end of the month. This produces a slightly more conservative estimate than an annuity-due (contributions at the start of each period).
Are the results guaranteed or just estimates?
These are estimates based on a constant interest rate. Real investment returns fluctuate year to year — a stock market index might average 7% over 30 years but return −20% in one year and +30% in another. The calculator is best used for planning and comparison, not as a guaranteed projection. For precise financial planning, consult a licensed financial advisor.
Explore More Calculators
Loan Calculator
Calculate your monthly mortgage or loan payment, total interest paid, and full amortization schedule. Supports PMI, HOA, taxes, and bi-weekly payments.
Calculate now →Percent Increase Calculator
Calculate the percentage increase between two numbers. Enter a starting and ending value to see the % increase and the absolute difference.
Calculate now →Ownership Calculator
Calculate how many shares or tokens you need to reach a target ownership percentage. Works for crypto circulating supply and stock shares outstanding.
Calculate now →Profit Percentage Calculator
Calculate profit amount and profit margin percentage from cost price and selling price. Instantly see how much you're making on any sale.
Calculate now →