Simple interest
Interest on a fixed amount that does not itself earn interest: I = P × r × t.
Simple interest is the principal times the yearly rate times the years. It does not add interest on interest. 1,500 at 4% for 3 years earns 1,500 × 0.04 × 3 = 180.
Classic Graphing 84
Start on the main screen: Press 2nd then mode (QUIT) to get back to the home screen. Pressing clear on a menu also backs out of it.
Type principal × rate × years and press enter. Write 4% as 0.04.
1500×.04×3enter
You should see180
Natural Scientific 991
Start on the main screen: Press MENU, then 1 (Calculate) to return to the main calculation screen. AC clears the line you are on.
Type principal × rate × years and press equals.
1500×.04×3=
You should see180
RPN Scientific 15
Start on the main screen: There is no menu to leave. Press the back arrow to clear a number you are typing, or CLx (g then back arrow) to clear the X register.
Key in the principal, ENTER, then the rate, and multiply.
1500ENTER.04×Key in the years and multiply again.
3×
You should see180.0000
RPN Financial 12 · Using the built-in simple-interest key (days)
Start on the main screen: There is no menu to leave: the display always shows the X register. Press f then R/S (P/R) to leave program mode, and clear a pending prefix by pressing ON.
Interest on 450 at 7% for 60 days: enter the days in n and the yearly rate in i.
60n7iStore the principal as a negative PV, then press f and i (INT).
450CHSPVfINTi
You should see5.25
The display shows interest on a 360-day year. Press x⇄y to see the principal (450). Press R↓ then x⇄y to see the 365-day interest instead. Press + after the first result to add the principal to the interest.