Simple Interest Calculator

Simple interest only ever accrues on the original principal - never on interest you have already earned. The formula is I = P x r x t. Example: K10,000 at 12% per year for 5 years earns K6,000 in simple interest. The alternative method, compound interest, lets each period's interest itself start earning interest in the next period. Under monthly compound interest, the same K10,000 at 12% over 5 years would earn K8,167 - K2,167 more than simple interest. That extra is the compounding effect.

Several everyday situations: microloans and kaloba (where lenders quote flat rates per month), ZRA penalties on overdue tax payments, promissory notes between businesses, the accrued interest portion of a bond between coupon payments, and some chilimba / round-robin savings schemes. Bank fixed deposits and most retail savings accounts use compound interest, not simple.

Microloan rates are often quoted per month, not per year. Pick "Monthly" in the selector and enter 5 - that gets stored as a 60% nominal annual rate (5 x 12 = 60%) and applied across your chosen term. The calculator supports Daily, Weekly, Bi-weekly, Monthly, Quarterly, Semi-annually, Annually rate quoting. Always convert to annual when comparing offers.

Simple interest only ever pays you on your original deposit. Compound interest pays you on your deposit plus all previously earned interest, so each period starts from a higher base. Over 5 years at 12% the gap is small (K2,167 on a K10,000 deposit). Over 20 years it explodes: simple earns K24,000 but compound monthly earns K98,925 - more than 4x the simple-interest total.

Yes - chilimba schemes, some savings clubs, and certain Zambian recurring-deposit accounts work this way. Each top-up earns simple interest only from when it was deposited until the end of the term, so later deposits accrue less interest. The same K500 monthly top-up over 5 years adds K8,850 in simple interest on top of the principal interest - compare that to K10,000 in additional growth under monthly compounding.

Example: K10,000 at 12% per year for 5 years. Interest = K10,000 x 0.12 x 5 = K6,000. Future value = K16,000. With a K500 monthly top-up over the same 5 years, total deposits are K40,000, total interest is K14,850, and the final balance is K54,850. Under monthly compound interest the same setup would reach K59,002 - the K4,152 gap is the cost of using simple interest.