Simulate lump-sum deposits or monthly regular investments, support custom compounding frequencies, and plot interest growth charts.
Simulate lump-sum deposits or monthly regular investments, support custom compounding frequencies, and plot interest growth charts. Use it for everyday work, development, learning, or quick verification.
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Compound interest means the interest itself earns interest. The future value of a lump sum is FV = P × (1 + r/n)^(n×t), where P is the principal, r the annual rate, n the number of compounding periods per year and t the number of years. For example, 100,000 at 2% compounded monthly for 10 years grows to about 122,100, while simple interest would give 120,000. The longer the term and the higher the rate, the wider the gap, which is why starting early matters more than saving a lot at once.
The calculator covers three common bank-deposit models. Lump sum (interest reinvested) is a single deposit whose interest is added to the principal and paid out at maturity, making full use of compounding. Interest payout pays the interest to you each period while the principal stays the same, so nothing compounds; it suits people who want steady cash flow. Regular saving adds a fixed amount every month and returns principal plus interest at the end, following PMT × [(1 + i)^N − 1] ÷ i, where i is the periodic rate and N the number of deposits.
Compounding frequency changes the real return. At a 2% nominal rate, annual compounding yields an effective 2.000% per year, quarterly about 2.015% and monthly about 2.018%. To compare offers fairly, convert them with effective annual rate = (1 + r/n)^n − 1. For a quick estimate use the Rule of 72: 72 ÷ annual return (%) ≈ years to double your money, so 6% doubles in about 12 years.
Results are nominal amounts that ignore inflation and tax. Interest is usually taxable income, and inflation steadily erodes purchasing power, so compare your rate with the inflation rate to see real growth. Investment returns are not fixed, so treat the projection as a planning aid, not a guaranteed outcome.
Future value = principal × (1 + annual rate ÷ periods per year)^(periods per year × years). 100,000 at 2% compounded monthly for 10 years becomes about 122,100.
At 2%, monthly compounding gives an effective annual rate of about 2.018% versus exactly 2% for annual compounding. Small at first, but it adds up on large balances over many years.
No. Because interest is paid out each period, the principal never grows, so the result equals simple interest.
Divide 72 by the annual return in percent to estimate how many years it takes to double your money: about 12 years at 6% or 24 years at 3%.
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