Compound Interest & Investment Growth Calculator
Compound interest grows your starting balance and each monthly deposit by the return rate, month after month. Enter principal, monthly contribution, expected return, years, and inflation to see nominal and inflation-adjusted future value.
Investment Growth
Forecasting & Planning
Fill all inputs
Your result appears here automatically as you type.
How the Investment Growth Works
Compound interest means you earn returns on your returns, so growth accelerates over time. This calculator compounds monthly: it multiplies the balance by one plus the monthly rate, then adds your contribution, repeating for every month. It also builds a parallel inflation-adjusted balance so you can see purchasing power, not just the headline number. In the example, 5,000 dollars plus 200 a month at 7% grows to about $124,379 in 20 years, or $84,468 in today dollars at 3% inflation. The gap shows why inflation matters for long horizons. Compounding frequency matters too: daily compounding produces slightly more than monthly at the same nominal rate. The rule of 72 estimates doubling time by dividing 72 by the annual rate. Start early, keep contributions consistent, and keep fees low, because a 1% fee can cost a large share of the final balance over decades. Avoid checking the balance daily, since compounding rewards patience, and the biggest gains usually arrive in the later years of a long horizon.
Formula Used
FV = P(1+r)^n + PMT x [((1+r)^n - 1) / r], with r = annual rate / 12 and n = months
$5,000 starting balance, $200 monthly, 7% annual return, 20 years, 3% inflation. Nominal future value = $124,379; inflation-adjusted value = $84,468.
When to Use This Calculator
- Projecting retirement savings with monthly contributions.
- Comparing investment accounts with different fees.
- Showing why starting early beats investing more later.
Common Mistakes
- Ignoring inflation: A large nominal balance can buy much less later; always check the real, inflation-adjusted figure.
- Forgetting fees: A 1% annual expense ratio compounds against you and can consume a meaningful share of long-term gains.
- Using an unrealistic return: Long-run stock returns average around 7% after inflation, so projecting 12% sets false expectations.
Frequently Asked Questions
How does compound interest differ from simple interest?
Simple interest pays only on the original principal. Compound interest pays on principal plus all previously earned interest, so the balance grows exponentially. Over long periods, that difference becomes very large and is the core reason to invest early.
What impact does compounding frequency have?
More frequent compounding means interest is added and starts earning sooner, so daily beats monthly and monthly beats annual at the same nominal rate. The difference is modest over short periods but grows over decades. This calculator compounds monthly.
What is the Rule of 72 and how does it work?
Divide 72 by the annual return rate to estimate how many years it takes to double your money. At 7%, money doubles roughly every 10.3 years. It is a quick mental shortcut for judging the power of a rate over time.
What is the formula for daily versus monthly compounding interest?
FV equals principal times (1 + rate/n) raised to n times years, where n is the periods per year. Daily uses 365 and monthly uses 12. At the same nominal rate, more frequent compounding produces a slightly higher result.
How long does it take for money to double with compound interest?
Use the rule of 72: divide 72 by the annual return. At 7%, money doubles in about 10.3 years, and at 10% in about 7.2 years. It is a fast way to judge how a rate plays out over long periods.
How This Page Is Reviewed
Written by the Recapflow Editorial Team and last reviewed . Every formula and worked example is cross-checked against the live calculator engine and a hand-worked example. This page is educational and does not replace professional financial, tax, or legal advice.