Compound interest works through a clean, powerful formula: FV = P × (1 + r)ⁿ. Every piece of your future wealth depends on just three variables: Principal (P), Rate (r), and Time (n).
Variable 1: Principal (P) — The Foundation
Principal is your starting investment. It has a linear effect on compound growth — double the principal, double the final result. But for long-term investors, principal is necessary but not the strongest factor.
Variable 2: Rate (r) — The Accelerator
Rate has an exponential effect. A tiny difference today becomes massive over decades. Going from 6% to 9% more than doubles your final wealth over 30 years. This is why improving your investment knowledge changes your financial life.
Variable 3: Time (n) — The Magic Maker
Time is the most powerful variable. Investing $1,000/month at 8%:
- Start at 25: ~$3,490,000 by age 65
- Start at 35: ~$1,500,000 by age 65
- Start at 45: ~$590,000 by age 65
Waiting just 10 years cuts your wealth by more than half. Time is the only variable you can never get back.
Priority by Life Stage
- 20s–30s: Time > Rate > Principal (start early!)
- 35–50: Rate > Time > Principal (boost returns)
- 50+: Principal > Rate > Time (rely on saved capital)