Calculate compound interest and year-by-year growth breakdown
A compound interest calculator shows how money grows when the interest it earns is added back to the balance and then earns interest itself. Unlike simple interest, which is paid only on the original amount, compound interest means each period's gain becomes part of the principal for the next — so growth accelerates over time. You enter a starting amount, a rate, how often it compounds and a number of years, and it returns the final balance, the interest earned, and a year-by-year breakdown of the climb.
The reason this calculator is worth using rather than a quick estimate is that compounding is genuinely hard to intuit: a modest rate over many years produces far more than multiplying the rate by the time would suggest, because of growth on top of growth. Seeing the year-by-year figures makes the "hockey stick" shape obvious and shows why starting early matters so much, and how regular contributions amplify the effect. This tool calculates everything in your browser, so the figures you enter stay private.
Simple interest is calculated only on the original principal, so it grows in a straight line. Compound interest is calculated on the principal plus accumulated interest, so each period builds on the last and growth accelerates — which is why compounding pulls ahead dramatically over long periods.
The more often interest is added, the sooner it starts earning interest itself. Monthly compounding beats annual at the same rate because gains are reinvested twelve times a year rather than once. The effect is real but usually modest compared to the impact of the rate and the time.
Because growth compounds on growth. Each year's interest joins the principal, so the base keeps getting larger and the absolute gains rise every year. Over decades this produces a curve that climbs far faster than the rate alone would suggest.
The calculation shows nominal growth — the raw balance before inflation and tax. Real purchasing power grows more slowly because inflation erodes value, and returns may be taxed, so treat the result as a gross projection rather than spendable money.
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