How to compare percentages with different denominators
Use three checks to interpret discounts, rates and aggregated results accurately.
Find the denominator
One group meets 9 of 10 deadlines and another meets 20 of 40. The group rates are 90% and 50%. To describe all deliveries together, add the numerators and denominators first. The overall rate is 29 out of 50, or 58%.
Separate percentage points from relative change
A rise from 50% to 60% is a gain of 10 percentage points. The relative rise is 10 divided by 50, or 20%. Label the measurement explicitly when you publish a report or update a spreadsheet.
Check in reverse
If a price after a 30% discount is €84, divide by 0.70 to find the original €120. Apply the discount to €120 to check your calculation. The same reverse check is useful when reviewing formulas in a spreadsheet.