Finance
Compound Interest Calculator
Project growth from a starting balance, monthly contribution, return rate, and time horizon. See contribution vs. interest split year-by-year.
How this is calculated
The compound interest formula with monthly contributions:
FV = P(1+r/n)^(nt) + PMT · [((1+r/n)^(nt) − 1) / (r/n)]
where P is starting principal, PMT is monthly contribution, r is annual rate, n is compounding periods per year (12 here), and t is years.
Real vs. nominal returns
For long-horizon planning, use realreturns (after inflation). The S&P 500 averages ~7% real over decades. Anything in nominal terms (~10%) overstates purchasing power.
Frequently asked
- The S&P 500's long-run real return averages ~7% after inflation. For projections, use real (inflation-adjusted) returns for a clearer picture.