How to Calculate Savings Growth With Compound Interest

Saving a little each month adds up to far more than the sum of your deposits, because compound interest pays you interest on your interest. The hard part is picturing how big that snowball gets over five, ten or twenty years. This guide shows how compound growth works and walks you through the Savings Calculator so you can project your future balance from a starting deposit and regular monthly contributions. It is free, instant and runs privately in your browser.

How compound savings growth works

Your balance grows from three sources: the money you start with, the money you add each month, and the interest earned on the whole pot. When interest compounds, each period it is calculated on the new, larger balance, so growth accelerates over time. The future value of regular deposits is:

FV = P x (1 + r)^n + M x (((1 + r)^n - 1) / r)

where P is the starting amount, M is the monthly deposit, r is the monthly interest rate (annual rate divided by 12), and n is the number of months. The first term grows your initial deposit; the second grows your stream of contributions.

How to use the Savings Calculator

Projecting your savings takes under a minute:

1. Open the Savings Calculator.
2. Enter your initial deposit (enter 0 if you are starting from scratch).
3. Enter your regular monthly contribution.
4. Enter the annual interest rate and the number of years.
5. Read your future balance, total contributions and total interest earned.

Try adjusting the monthly amount or the number of years to see how much difference small changes make. Increasing the contribution by even 50 dollars a month can add thousands to your final balance over a long horizon.

A worked example with real numbers

Suppose you start with 1,000 dollars, add 200 dollars a month, and earn 5% a year for 10 years.

• Total you contribute: 1,000 + (200 x 120) = 25,000 dollars
• Future balance: about 32,300 dollars
• Interest earned: about 7,300 dollars

You put in 25,000 dollars but end with over 32,000 dollars. Stretch the same plan to 20 years and the balance climbs to roughly 84,000 dollars, of which more than 35,000 dollars is interest. The longer you leave it, the more compounding does the heavy lifting.

Use cases for a savings projection

A savings calculator helps you plan for almost any goal:

• Building an emergency fund of three to six months of expenses
• Saving a house deposit by a target date
• Putting money aside for a wedding, car or holiday
• Long-term goals like a child's education
• Checking whether your current monthly saving will reach a target

For goals tied to higher-rate accounts or investments, compare results with the Compound Interest Calculator to see how the compounding frequency changes the outcome.

Tips and common mistakes

Get a realistic projection by keeping these in mind:

• Use a realistic rate. Ordinary savings accounts pay far less than long-term stock market averages; do not over-estimate.
• Account for inflation. A balance in 20 years buys less than the same number today, so treat projections as nominal.
• Be consistent. The model assumes you keep contributing every month; skipped deposits lower the result.
• Start early. Time is the biggest factor in compounding, far more than the rate or the amount.

Explore more money tools in calculators or see all tools.

Private and free in your browser

The Savings Calculator runs entirely in your browser. Your figures are never uploaded or stored on a server, so your financial plans stay private. There is no sign-up and no limit. Use the Savings Calculator as often as you like to test different scenarios and find a plan you can stick to.