Defense is a player statistic that determines how much damage can be taken per hit. On non-Expert mode worlds, the damage the player takes is reduced by half of their defense value, altogether. In Expert mode, damage the player takes is reduced by three-quarters of their defense value, rounded up. Defense can be increased by equipping armor and accessories, or temporarily boosted by various buffs. No attack can be reduced below 1 damage (with the exception of a player with an ally wearing the Paladin's Shield).
Some forms of damage are impossible to reduce through defense. Damage from health-draining Debuffs like Cursed Inferno, drowning in water, or colliding with a boulder are not reduced by defense.
Damage taken from lava can be reduced through defense.
Mechanics
Defense gives a flat reduction in damage: i.e. damage is reduced by a fixed amount per hit (as opposed to a multiplicative damage reduction, which would reduce damage by a percentage).
Normal mode Formula
The formula is:
net damage = attack - (defense * 0.5)
For example:
- With 20 Defense, a 40 Damage attack is reduced by 10, resulting in 30 damage taken.
- With 30 Defense, a 40 Damage attack is reduced by 15, resulting in 25 damage taken.
Expert mode Formula
In expert mode, the formula is:
net damage = attack - (defense * 0.75)
For example:
- With 20 Defense, a 40 Damage attack is reduced by 15, resulting in 25 damage taken.
- With 30 Defense, a 40 Damage attack is reduced by 23, resulting in 17 damage taken.
Note that in expert mode only the player's defense follows the formula. Enemies will still take the same amount of damage as in normal mode.
Enemies
Enemies have the same Defense mechanics as players. Monsters with high defense will take virtually no damage from low damage weapons (e.g. Fire Imps take 5 damage from the Minishark with Musket Balls). Accordingly, when fighting high defense monsters, high damage weapons are preferable.
Armor
Defense boosts
Here is a list of accessories, and their respective defense bonuses. A list of armor including defenses can be found on the armor page.
| Item | Accessory Defense |
|---|---|
 Shackle |
1 |
 Cobalt Shield |
1 |
 Obsidian Skull |
1 |
 Shield of Cthulhu |
2 |
 Obsidian Shield |
2 |
 Moon Charm |
3 (only during the night) |
 Moon Shell |
3 (only during the night) |
 Moon Stone |
4 (only during the night) |
 Sun Stone |
4 (only during the day) |
 Celestial Stone |
4 |
 Ankh Shield |
4 |
 Paladin's Shield |
6 (Absorbs 25% of damage done to players on your team
Only active above 25% life) |
 Celestial Shell |
4 (during the day)
7 (during the night) |
 Flesh Knuckles |
7 |
 Frozen Turtle Shell |
0 until below 50% health when it reduces total damage by 25% 
30 (When below 25% health) |
| Modifiers | 4 (Max per accessory) |
| Buff / Debuff | Temporary Defense |
 Well Fed |
2 |
 Dryad's Blessing (Buff)
|
8 |
 Ironskin |
8 |
 Tipsy |
Defense reduced by 4 |
 Weak |
Defense reduced by 4 |
 Ichor (debuff) |
Defense reduced by 20 |
 Broken Armor |
Defense reduced by half |
Damage reduction boosts
| Buff | Source | Damage reduction bonus |
|---|---|---|
 Solar Blaze |
Solar Flare armor | 30% |
 Beetle Endurance |
Beetle armor | 15%/30%/45% |
 Paladin's Shield |
Paladin's Shield | 25% (Only active above 25% life) |
 Endurance |
Endurance Potion | 10% |
 Ice Barrier |
Frozen Turtle Shell | 0   / 25% (When below 50% health)
|
 Warmth |
Warmth Potion | 30% (Reduces damage only from cold-themed enemies) |
| Item | Source | Damage reduction bonus |
 Worm Scarf |
Treasure Bag (Eater of Worlds) | 17% |
Armor Penetration
Armor penetration is a statistic that reduces the defense of the player's targets. For instance, a Pixie normally has 20 defense. If the player has 5 Armor Penetration, then the Pixie will be taken to have 15 defense instead.
| Source | Armor penetration bonus |
|---|---|
 Shark Tooth Necklace |
5 |
 Sharpening Station |
4 for Melee Weapons only |
Notes
Reason: "Needs version separation"
- The highest possible defense is 165 normally, and 173 in expert mode.
- Chlorophyte Mask，Solar Flare Breastplate and Solar Flare Leggings or Vortex Leggings - 79 defense
- Flesh Knuckles - 7 defense
- Celestial Shell - 7 defense if worn at night
- Paladin's Shield - 6 defense
- Guarding with the Brand of the Inferno - 20 defense
- Any other two accessories that give 4 defense at night - 8 defense
- Warding modifiers on all accessories - 20(normal)/24(expert) defense
- Ironskin buff - 8 defense
- Well fed buff - 2 defense
- The Dryad's Blessing grants an additional 8 defense.
- Riding a Mechanical Cart at full speed gives an additional 7 defense (expert mode only, but can be imported to a normal world). - However, you cannot guard with the Brand of the Inferno while riding a Mechanical Cart.
- Any sixth accessory that gives 4 defense at night, with a Warding prefix (expert mode only).
- The highest damage reduction is 87%.
- Armor-based reductions are multiplicative.
- Beetle armor with shell - 45% reduction
- Accessory- and potion-based reductions are additive.
- Frozen Turtle Shell - 25% reduction
- Worm Scarf - 17% reduction
- Endurance Potion - 10% reduction
- Paladin's Shield buff - 25% reduction
- Armor-based reductions are multiplicative.
(100%-45%) * (100%-(25%+17%+10%+25%)) = 12.7% damage taken = 87.3% damage reduction
Trivia
- Although not possible in-game, if a piece of armor were to gain a prefix, it would apply the effects just like an accessory would. For example, a set of Warding modified armor would add 12 defense total; each piece adds 4 defense to the total.