Compound Growth Calculator - Investment Growth Forecast

Compound growth is the process that turns a starting balance into a larger future value when earnings are reinvested. The compound growth calculator is built for that planning question: if money earns a stated annual rate and those earnings stay in the account, what might the balance be after a chosen number of years? Investors use it for brokerage accounts, business owners use it for retained cash, and households use it for emergency funds, education savings, and retirement targets. The result is a deterministic projection from the figures you enter, not a market forecast or a guaranteed return. The future value of a lump sum is P × (1 + r/n)^(n t), where P is principal, r is the annual rate as a decimal, n is compounding periods per year, and t is years. When you also add a contribution at the end of each compounding period, the calculator appends the ordinary annuity factor: PMT × [((1 + r/n)^(n t) − 1) / (r/n)]. If the rate is zero, contributions simply accumulate as PMT × n × t. Interest earned is future value minus principal minus total contributions. Percentages are converted to decimals before the exponent is applied, and a blank contribution is treated as zero. That structure matches how savings accounts, certificates of deposit, and many investment plans actually credit interest: more frequent compounding raises the effective yield slightly relative to the same nominal rate compounded annually. Monthly contributions interact with monthly compounding, which is why the contribution field is an amount per compounding period rather than a separate calendar schedule. A $200 contribution with monthly compounding is $200 each month; with annual compounding it is $200 once a year. Keep the contribution unit aligned with the frequency you select so the projection stays honest. Common uses include setting a savings target, comparing a higher rate against a longer horizon, and testing whether a planned monthly deposit is large enough to reach a round number. Small rate changes compound into large dollar gaps over long horizons, which is why scenario testing matters. Run a cautious case, a base case, and an optimistic case, changing one input at a time. The supporting interest figure shows how much of the ending balance is earnings rather than money you deposited. Caveats are important. The projection ignores taxes, account fees, inflation, contribution pauses, and sequence-of-returns risk. A quoted annual percentage yield may already embed compounding, so do not compound an APY a second time. For taxable accounts, after-tax growth is lower than the pre-tax rate. For retirement planning, employer matches and inflation-adjusted spending needs sit outside this formula. Use current statements for principal, a realistic rate rather than a best-case year, and treat the future value as a planning estimate to discuss with an adviser when the decision is large. Record the assumptions, revisit them when rates or goals change, and let the compound growth calculator make the arithmetic transparent so the judgment call stays yours.