See how your money grows over time — with or without monthly contributions.
Compound interest means your interest earns interest. Unlike simple interest — where you only earn on your original principal — compounding grows your balance exponentially over time. The longer your money is invested, the more dramatic the effect becomes.
Albert Einstein (allegedly) called it the eighth wonder of the world. Whether or not he actually said that, the math is unambiguously powerful.
Where: P = Principal, r = annual rate (decimal), n = compounding periods per year, t = years, PMT = contribution per compounding period.
Compounding monthly versus annually can meaningfully change your final balance over long periods. Daily compounding ekes out a small extra gain over monthly, but the difference shrinks the more frequently you compound. The bigger lever is always the rate and the time horizon.
A 25-year-old investing $10,000 at 7% for 40 years ends up with roughly $150,000. A 35-year-old investing the same amount for 30 years ends up with about $76,000. Same money, same rate — a decade of difference cuts the outcome nearly in half. Start earlier. That's the whole lesson.
Even modest monthly contributions dramatically accelerate wealth accumulation. Adding $200/month to a $10,000 principal at 7% for 20 years turns $58,000 in total contributions into over $120,000 — the interest nearly doubles your money on top of what you put in.