Why compound interest matters
The mechanic is simple: each period, interest is calculated on the current balance — which already includes interest from earlier periods. The result is exponential growth, not linear. Over 5 years, the difference vs simple interest is minor. Over 30 years, it is enormous — often double or triple.
Time is the dominant variable, not the rate. Someone who starts saving at age 25 with ₦10,000/month at 12% APR ends up with about ₦12.8M at age 55 (30 years). Someone who starts at 35 with the same contribution and same rate ends with about ₦3.9M at 55 (20 years). The extra 10 years more than triple the result — not because the person contributed more, but because the first years of compounding had time to grow.
That is why starting early with less almost always beats starting late with more. For young African salary earners, the practical conclusion: open a pension RSA, money market fund, or fixed deposit this year, even with a small monthly amount. Increase as your income grows. Time does the rest.
A useful framing: the rule of 72. Divide 72 by your annual rate to estimate how many years it takes your capital to double with no new contributions. At 8% APR, your money doubles in about 9 years. At 12% APR, in 6 years. At 6% APR, in 12 years. This mental shortcut is accurate within about 1% for most rates between 5% and 20%, and it is useful for quick mental math when you do not have the calculator open. Paired with a long horizon, it makes the difference between savings and investment vivid.
A final intuition worth holding: compounding frequency is widely overrated in popular conversations. The difference between daily, monthly, and annual compounding is almost always marginal over 30 years — under 3% divergence in typical cases. What actually matters: the nominal rate, the regularity of your contributions, and the number of years you leave the mechanism running. Do not optimise the frequency; optimise the start date.