Question 1

How do you calculate percentage change?

Accepted Answer

Subtract the original value from the new value, divide by the original value, and multiply by 100. For example, from 80 to 100 is (100 − 80) ÷ 80 × 100 = +25%. A positive result is an increase and a negative result is a decrease. The change is always measured relative to the original, older number.

Question 2

What is the difference between percentage change and percentage points?

Accepted Answer

Percentage change is the relative change between two numbers. Percentage points measure the simple difference between two percentages. If a rate rises from 5% to 6%, that is a 1 percentage point increase but a 20% percentage change, because 1 ÷ 5 × 100 = 20%.

Question 3

Why can't I calculate a percentage change from zero?

Accepted Answer

Percentage change divides by the original value, and dividing by zero is undefined. If the starting value is 0, any increase is infinitely large in percentage terms, so the result has no meaning. The calculator flags this instead of showing a misleading number.

Question 4

How do I increase or decrease a number by a percentage?

Accepted Answer

To increase a value by a percentage, multiply it by 1 plus the percentage as a decimal — to add 10%, multiply by 1.10. To decrease, multiply by 1 minus the decimal — to take off 10%, multiply by 0.90. The Adjust mode in this calculator does this for you and shows the change amount.

Change	Result	Difference
-50%	40	-40
-25%	60	-20
-10%	72	-8
-5%	76	-4
+5%	84	+4
+10%	88	+8
+25%	100	+20
+50%	120	+40
+100%	160	+80