Definitions
From an old value A to a new value B, the relative change is (B − A) / A. Express that as a percent by multiplying by 100. Increase when B > A; decrease when B < A.
percent change = (B − A) / A × 100%
Why the base is sacred
Going from $50 to $75 is a 50% increase. Going from $75 to $50 is a 33.3% decrease. Same dollar move, different percentage—because the denominator changed.
Multipliers
A p% increase multiplies by (1 + p/100). A p% decrease multiplies by (1 − p/100). Chaining changes multiplies the multipliers—not the percents.
Headline traps
“Stocks rose 100% after falling 90%” still leaves you below the old peak. Always recompute from the actual prior price, not from a rough memory of the headline.
Use the calculator
FAQ
- What’s the difference between points and percent change?
“Points” add to a rate (3% to 5% is +2 points). “Percent change” compares relative to a starting value and is not additive across unrelated bases.