Damage

Damage refers to the amount of damage each tear deals to enemies, and is represented by a sword. As damage increases, the size of the tears increases as well. However, tear size is not always a valid indication of how much damage your tears will do. Tears will grow and shrink when your damage changes, but tears of a certain size do not have a specific damage value, and two tears of the same size (in two different runs) are likely to have different damage values.

Polyphemus is an example of an item which provides a very high Damage stat.

Effective Damage

The formula for damage is: File:Effective Damage Formula.png

where:

CharBaseDmg = 3.5 multiplied by a particular Character Modifier,
TotalDmgUps = the total of all regular damage ups collected (not including special exceptions or damage multipliers),
FlatDmgUps = the total of all damage ups that are excluded from the above (for example, Curved Horn or Ipecac), and
EffectiveDmg = the approximate damage that can be expected per tear, or per 'tick' when using Brimstone or Technology 2.

This formula makes most damage upgrades less potent the more that Isaac has. For example, a Pentagram on Isaac would make his total damage (1 * 1.2 + 1)^0.5 = 1.48 * 3.5 = 5.19. Another Pentagram increases this to 6.45 (a 1.26 increase instead of a 1.69 increase). The higher a character's base damage, the more effective Damage Ups will be for that character. Flat damage modifiers and special adjustments like Polyphemus or Sacred Heart happen after the main formula.

Character Modifier

The character base damage of each tear is calculated multiplying the base damage of 3.50 with each character's damage modifier. These character modifiers are:

Eve^†: 0.75 • 3.50 = 2.625 per tear
Isaac, Magdalene, Samson, Lazarus, Eden, Lilith, The Lost, Apollyon, and The Soul: 1.00 • 3.50 = 3.50 per tear
???: 1.05 • 3.50 = 3.675 per tear
Keeper, Cain and Revived Lazarus: 1.20 • 3.50 = 4.20 per tear
Judas: 1.35 • 3.50 = 4.725 per tear
Azazel: 1.50 • 3.50 = 5.25 per beam tick
The Forgotten: 1.50 • 3.50 = 5.25 base bone club damage
Dark Judas: 2 • 3.50 = 7.00 per tear

^†: Whore of Babylon has the unique effect of increasing Eve's damage modifier from 0.75 to 1.00 when active. This does not apply to other characters, however.

Damage Multipliers

Some items multiply damage rather than simply adding to it. Damage multipliers do not simply multiply the character's damage once; the damage stat is constantly recalculated and the damage multipliers are multiplied with the end result. This means that if a character starts with 3.50 damage and gets a 2x multiplier, their effective damage will be 3.5*2 = 7.00. If an item that grants +1 damage is picked up, the character's effective damage will be 3.5*(1*1.2+1)^0.5*2 = 3.5*(2.2)^0.5*2 = 3.5*1.48*2 = 10.38, and not 7.00 + 1.

Most damage multipliers stack; for example, Proptosis and Eve's Mascara both provide a 2x multiplier, and picking up both will give a total multiplier of 4x. The exception to this is the 1.5x damage multipliers provided by Cricket's Head, Magic Mushroom, and the combination of Blood of the Martyr and The Book of Belial. These multipliers do not stack; for example, picking up both Cricket's Head and Magic Mushroom will result in an overall 1.5x multiplier rather than the expected 2.25x.

Items that affect damage

Activated Items

Passive Items

Trinkets

Other

In co-op, Rage Baby, Revenge Baby, and Belial Baby will occasionally briefly increase damage. Dark Baby will occasionally briefly increase all stats, including damage. Buddy Baby will occasionally briefly grant the Guillotine effect, which increases damage. Whore Baby will occasionally briefly grant the Whore of Babylon effect, which increases damage.
The III - The Empress card activates the Whore of Babylon effect for the current room, which increases damage.
The XI - Strength card activates the Magic Mushroom effect for the current room, which increases damage.
The XV - The Devil card activates The Book of Belial effect for the current room, which increases damage.
The Huge Growth card increases damage, range, and Isaac's size for the current room.

The Binding of Isaac: Rebirth