Interés Compuesto
Proyecta cómo crece un saldo cuando el interés genera interés sobre sí mismo.
The compound interest calculator projects how a principal (plus any regular contribution) grows over time when interest is earned on both the original balance and all previously accumulated interest.
Introduce un porcentaje entero — por ejemplo 6 para 6%.
12 = mensual, 4 = trimestral, 1 = anual.
Cantidad opcional añadida al final de cada período.
Ejemplo resuelto
Usando los valores anteriores:
- Capital
- 1000 €
- Tasa de interés anual
- 600,0 %
- Períodos de capitalización por año
- 12
- Años
- 10
- Aportación periódica
- 0 €
The formula
Variables
- Final balance (€)
- Principal (starting balance) (€)
- Annual interest rate (%)
- Compounding periods per year
- Periodic rate (r ÷ n)
- Total number of periods (n × years)
- Contribution added each period (€)
What compound interest means
Compound interest is interest earned on interest. Put money in an account that pays interest, and after the first period the balance is bigger than the principal — the _next_ period's interest is then calculated on that larger balance, not just the original amount. Over enough time, the interest earned on previously-earned interest starts to dwarf the interest earned on the original principal, which is why compound growth accelerates the longer money stays invested.
This is the single most important idea behind long-term saving, retirement planning, and loan amortization, and it's why starting to invest early matters more than almost any other single decision.
How to calculate it
- Convert the annual rate to a periodic rate by dividing it by the number of compounding periods per year (monthly compounding at 6% annual is a 0.5% periodic rate).
- Multiply the number of years by the compounding periods per year to get the total number of periods.
- Apply the periodic rate to the balance every period, and — if you're contributing regularly — add the contribution at the end of each period before compounding continues.
- Interest earned is simply the final balance minus the principal and minus everything you contributed along the way.
- More frequent compounding (monthly vs. annual) very slightly increases the final balance for the same stated annual rate.
- A periodic contribution turns a one-time deposit into an ordinary annuity — a series of regular deposits that each compound for whatever time remains until the end of the term.
A worked example
€1,000 invested at a 6% annual rate, compounded monthly, for 10 years, with no additional contributions: the periodic rate is 6% ÷ 12 = 0.5% per month over 120 months. Compounding €1,000 at 0.5% per month for 120 months grows the balance to approximately €1,819, meaning about €819 of that final balance is interest — nearly as much as the original principal, purely from letting the balance compound for a decade.
Limitations to know
This calculator assumes a fixed rate and a fixed contribution for the entire term — real savings rates change, and real contributions often grow with income. It also doesn't account for taxes or fees, which can meaningfully reduce real-world compounding, especially in taxable accounts where interest is taxed each year rather than left to compound tax-free.