Percent is specific and is usually used with a number.
- They expect to reduce their workforce by 15 percent.
Percentage is not specific and is never used with a number.
- The reduction affects a small percentage of engineers.
Note: Percent should be spelled as one word (not per cent). Also, percent is becoming accepted without a number by it.
- What percent of your workday is spent in meetings?
Percentage point is the correct phrase when referring to a change in a figure that is already a percentage. One percentage point is always 1/100th of the total.
- The President’s approval rating fell from 43 percent to 40 percent, a drop of three percentage points (not 3 percent).