Basics
DICE
Dice rolls are described with expressions such as "3d4+3," which means "roll three four-sided dice and add 3" (resulting in a number between 6 and 15). The first number tells you how many dice to roll (adding the results together). The number immediately after the "d" tells you the type of die to use. Any number after that indicates a quantity that is added or subtracted from the result.
d%: Percentile dice work a little differently. You generate a number between 1 and 100 by rolling two different ten-sided dice. One (designated before you roll) is the tens digit. The other is the ones digit. Two 0s represent 100.
ABILITIES
Six abilities provide a quick description of every creature's physical and mental characteristics:
- Strength, measuring physical power
- Dexterity, measuring agility
- Constitution, measuring endurance
- Intelligence, measuring reasoning and memory
- Wisdom, measuring perception and insight
- Charisma, measuring force of personality
Is a character muscle-bound and insightful? Brilliant and charming? Nimble and hardy? Ability scores define these qualities - a creature's assets as well as weaknesses. The three main rolls of the game - the ability check, the saving throw, and the attack roll - rely on the six ability scores.
ABILITY MODIFIERS
Almost all actions that you take are associated with one of the six abilities. Each ability has a modifier ranging from -5 to +5. These modifiers are usually applied to the base score used to perform these actions.
| Ability Scores and Modifiers | |
|---|---|
| Score | Modifier |
| 1 | -5 |
| 2-3 | -4 |
| 4-5 | -3 |
| 6-7 | -2 |
| 8-9 | -1 |
| 10-11 | +0 |
| 12-13 | +1 |
| 14-15 | +2 |
| 16-17 | +3 |
| 18-19 | +4 |
| 20-21 | +5 |
| 22-23 | +6 |
| 24-25 | +7 |
| 26-27 | +8 |
| 28-29 | +9 |
| 30 | +10 |
THE CORE MECHANIC
Whenever you attempt an action that has some chance of failure, you roll a twenty-sided die (d20). To determine if your character succeeds at a task you do this:
- Roll a d20.
- Add any relevant modifiers.
- Compare the result to a target number.
If the result equals or exceeds the target number, your character succeeds. If the result is lower than the target number, you fail. In most cases, rolling a 20 ("natural 20" or "critical hit") always indicates success and rolling a 1 ("natural 1" or "critical fail") indicates failure. Skill checks are the exception to this rule, as there are some tasks that you just don't have the skill to do, no matter how lucky you are.
The target for most dice rolls is the Difficulty Class (DC). The DC is a number that you must score as a result in order to succeed. The DC is usually set by the Game Master based on guidelines laid out in the rules. For attack rolls, the DC is equivalent to your opponent's modified Amor Class.
For some skill checks, the DC is set when an opponent performs a skill check of their own. For instance, when attempting to deceive an opponent your Deception roll sets the DC for any attempting an Insight to hit. Likewise, stealth sets DCs for perception, Traps checks set the DC to disarm a trap, and Rope Use sets a DC for untying a knot. Even Craft skills help set a DC for the quality of some items (like a lock). These DCs are usually set by whomever performs the skill check first, and are opposed by those attempting to beat them, even if the rolls are nearly simultaneous.
MODIFERS
Usually when you roll d20 to perform an action, you will also add modifiers to the dice roll. Modifiers are numbers that you will add or subtract from the dice roll to get your final result. Positive modifiers are often called bonuses, and negative modifiers are called penalties.
Modifiers represent anything about your circumstances that might increase or decrease your chance of success. Modifiers might represent the amount of training you have in a certain skill, unfavorable circumstances that you happen to be in, a temporary condition that boosts your competence, or any number of factors. In short, for better or worse, modifiers are what make your attempt to perform an action more than just mere chance.
There are many types of modifiers, but they all fall into a few general categories. Basically, any roll you make fits the following pattern.
d20 + Base Score + Competence Bonus + Circumstance bonus - any penalties
Penalties always stack, no matter where they come from or what type they are. However, you can only have one competence bonus and one circumstance bonus. If you have multiple effects that give you bonuses of the same type, use the largest one.
BASE SCORES
Your base scores represent your training and skill in performing a certain action. Here are a few of the most common types of base scores.
- Skill Scores - How well you can perform a certain skill
- Knowledge Scores - How much you know about a certain topic.
- Saving Throw Bonuses - How good you are at avoiding certain types of negative conditions.
- Strength Attack Bonus - How well you do strength-based attacks
- Dexterity Attack Bonus - How well you do dexterity-based attacks
- Spell Attack Bonus - How well you attack with spells
- Armor Class (AC) - How well you defend yourself
Different methods are used to calculate each of these scores. The details of how to calculate and use each of these scores can be found elsewhere. However, a few general concepts might be helpful in understanding how they function.
- Score Growth:
Scores grow in one of two ways, either automatically as you level up or by adding ranks to them. Combat scores tend to grow automatically. Skills, knowledge, and saving throws require you to manually add ranks.- Ability Modifiers:
Most base scores are modified by your ability modifiers (see above)- Enhancements:
Enhancements can also boost your base score. These usually affect your AC, ability scores, or combat bonuses. No two enhancements may boost the same score. If you have two in effect, take the larger enhancement.
ADVANTAGE AND DISADVANTAGE
Sometimes a special ability or spell tells you that you have advantage or disadvantage on an ability check, a saving throw, or an attack roll. When that happens, you roll a second d20 when you make the roll. Use the higher of the two rolls if you have advantage and use the lower roll if you have disadvantage. For example, if you have disadvantage and roll a 17 and a 5, you use the 5. If you instead have advantage and roll those numbers, you use the 17.
If multiple situations affect a roll and each one grants advantage or imposes disadvantage on it, you don't roll more than one additional d20. If two favorable situations grant advantage, for example, you still roll only one additional d20.
If circumstances cause a roll to have both advantage and disadvantage, you are considered to have neither of them, and you roll one d20. This is true even if multiple circumstances impose disadvantage and only one grants advantage or vice versa. In such a situation, you have neither advantage nor disadvantage. When you have advantage or disadvantage and something in the game, lets you reroll the d20, you can reroll only one of the dice. You choose which one.
You usually gain advantage or disadvantage through the use of special abilities, actions, or spells. The GM can also decide that circumstances influence a roll in one direction or the other and grant advantage or impose disadvantage as a result.
FAVOR
Sometimes an ability will allow you roll a certain action with favor. Favor simply means that if you miss the DC of an action by 1, you still succeed.
D4 BONUS
Instead of a straight numerical bonus, some effects grant a d4 bonus. In such cases, you simply roll your dice, as usual, but also roll 1d4 and add it to the rest of your dice. If you are rolling at advantage or disadvantage, do not reroll the d4. You may also take a d4 penalty, which functions the same way except that 1d4 is subtracted from your dice roll.
ROUNDING FRACTIONS
In general, if you wind up with a fraction, round down, even if the fraction is one-half or larger. Certain rolls, such as damage and hit points, have a minimum of 1.