Step 4: Degrees of Success
Source Player Core pg. 393
Many times, it's important to determine not only if you succeed or fail, but also how spectacularly you succeed or fail. Exceptional results—either good or bad—can cause you to critically succeed or critically fail at a check.
You critically succeed when the check's result meets or exceeds the DC by 10 or more. If the check is an attack roll, this is also known as a critical hit. You can also critically fail a check. The rules for critical failure—sometimes called a fumble—are the same as those for a critical success, but in the other direction: if you fail a check by 10 or more, that's a critical failure.
Some actions and abilities have stronger effects on a critical success or failure. For example, a Strike deals double damage on a critical hit. If an effect doesn't list a critical success effect, the critical success effect is the same as the success effect, and the same goes for critical failures.
You critically succeed when the check's result meets or exceeds the DC by 10 or more. If the check is an attack roll, this is also known as a critical hit. You can also critically fail a check. The rules for critical failure—sometimes called a fumble—are the same as those for a critical success, but in the other direction: if you fail a check by 10 or more, that's a critical failure.
Some actions and abilities have stronger effects on a critical success or failure. For example, a Strike deals double damage on a critical hit. If an effect doesn't list a critical success effect, the critical success effect is the same as the success effect, and the same goes for critical failures.
Natural 1 and Natural 20
Source Player Core pg. 393
If you rolled a 20 on the die (a “natural 20”), your result is one degree of success better than it would be by numbers alone. If you roll a 1 on the d20 (a “natural 1”), your result is one degree worse. This means that a natural 20 usually results in a critical success and natural 1 usually results in a critical failure. However, if you were going up against a very high DC, you might get only a success with a natural 20, or even a failure if 20 plus your total modifier is 10 or more below the DC. Likewise, if your modifier for a statistic is so high that adding it to a 1 from your d20 roll exceeds the DC by 10 or more, you can succeed even if you roll a natural 1!
Certain abilities can change the degree of success on a roll. When resolving such an ability, apply the adjustment from a natural 20 or natural 1 before anything else.
Certain abilities can change the degree of success on a roll. When resolving such an ability, apply the adjustment from a natural 20 or natural 1 before anything else.