Savings Calculators

Compound Interest Calculator

Project the future value of savings or investments with monthly contributions and compound growth.

Year-by-year projection uses period-by-period compounding — the same way real accounts grow.

$
$
%
yr
Projected value in 25 years
$354,546
Compound growth alone: $229,546.
Total contributed
$125,000
Interest earned
$229,546
Year-by-year growth
YearContributedInterestBalance
1$4,800$547$10,347
2$4,800$934$16,081
3$4,800$1,348$22,230
4$4,800$1,793$28,823
5$4,800$2,270$35,892
6$4,800$2,781$43,473
7$4,800$3,329$51,602
8$4,800$3,916$60,318
9$4,800$4,546$69,664
10$4,800$5,222$79,686
11$4,800$5,946$90,433
12$4,800$6,723$101,956
13$4,800$7,556$114,312
14$4,800$8,450$127,562
15$4,800$9,407$141,769
16$4,800$10,434$157,004
17$4,800$11,536$173,339
18$4,800$12,717$190,856
19$4,800$13,983$209,639
20$4,800$15,341$229,780
21$4,800$16,797$251,377
22$4,800$18,358$274,535
23$4,800$20,032$299,367
24$4,800$21,827$325,994
25$4,800$23,752$354,546
Overview

How the Compound Interest Calculator Works

Compound interest is the most important concept in personal finance. This calculator projects how an initial deposit plus monthly contributions grow over time at a given rate, with a year-by-year breakdown so you can see how dramatically growth accelerates in the later years.

Formula

The Math Behind the Calculator

Each period: balance grows by (balance × periodic rate) and then a contribution is added. Over many periods this produces exponential growth. Approximation: FV = P(1 + r/n)^(nt) + PMT × [((1 + r/n)^(nt) − 1) / (r/n)].

Example

A Worked Example

$5,000 starting balance, $400 monthly contribution, 7% annual return, 25 years: final value ≈ $337,000. Total contributed: $125,000. Compound interest earned: $212,000 — more than the contributions themselves.

How to use

How to Use the Compound Interest Calculator

  1. 1Enter your starting balance (zero is fine).
  2. 2Add a realistic monthly contribution — something you'll stick with.
  3. 3Use a long-term return assumption appropriate for your account: 4–5% for HYSAs and CDs, 6–8% for diversified stock-heavy portfolios.
  4. 4Set a time horizon that matches the goal (retirement, college, house down payment).
Interpretation

What the Results Mean

  • Future value is the projected balance at the end of the horizon.
  • Total contributions is what you actually deposited.
  • Total interest is the growth — the longer your horizon, the larger this share becomes.
Avoid

Common Mistakes to Avoid

  • Using a savings rate (4%) for stock-market projections, or a stock-market rate (10%) for a savings account.
  • Skipping years because 'I'll start later' — early years compound the longest.
  • Forgetting taxes and inflation, which both reduce real returns.
Keep going

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FAQ

Frequently Asked Questions

Is 7% realistic?+

It's a reasonable long-term assumption for a diversified stock-heavy portfolio (S&P 500 historical real return is roughly 6–7%). Adjust based on your asset allocation.

Are taxes included?+

No — this is a pre-tax projection. Tax-advantaged accounts (401k, IRA, Roth) preserve more of the growth.

What about inflation?+

Not included. To estimate real (inflation-adjusted) growth, subtract roughly 2–3% from your return assumption.

Financial Disclaimer

This calculator is for educational and estimation purposes only. It does not provide financial, mortgage, tax, investment, or legal advice. Actual rates, payments, taxes, fees, insurance costs, eligibility, and loan terms vary by lender, location, credit profile, and market conditions. Always compare official offers and consult a qualified professional before making financial decisions.

Last updated June 2026 · Prepared by the mCalculator Editorial Team