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How to Calculate THACO

To simplify the Advanced Dungeons and Dragons (AD&D) rule set for the 2nd edition of the game, the game designers developed a new system to determine hits landed on opponents during combat. THAC0, to hit armor class 0, allowed a simple calculation for determining hit chances based on a player character's THAC0 number. This was the number a player needed to roll to hit an opponent with an armor class of 0. Knowing this number, players of the 2nd edition could easily determine the roll needed to hit other armor classes, negating the need to look up each hit roll on a chart during gameplay.

Things You'll Need

AD&D 2nd Edition Dungeon Master's Guide
AD&D 2nd Edition Player's Handbook
AD&D 2nd Edition Monster's Manual

Instructions

- 1
  Open the AD&D 2nd Edition Dungeon Master's Guide and turn to Chapter 9, the "Combat" chapter. Locate tables 37, 38 and 39 to consult when calculating THACO.
- 2
  Find the player character class group on the left side of Table 38, "Calculated THAC0S." Each specific character class falls within one of the four basic groups, Priest, Rogue, Warrior and Wizard, Consult the AD&D 2nd Edition Player's Handbook to determine which group the player's character falls under. Move to the right along the table until you find the player's level. The number listed under level is the player character's THACO. To hit an opponent with an armor class of 0, you need to roll this or a higher number on a 20-sided die. Player class and levels are listed on the player's Character Sheet.
- 3
  Use Table 37, "THAC0 Advancement" for player characters over the experience level of 20. Locate the character group. Use the ratio listed under "Improvement Rate Points/Level" to modify the character's THAC0 for each level over 20. For example, a ratio of 1/3 means you subtract one THAC0 point for each three levels earned. So a Wizard with a THAC0 of 14 at level 19, has a THAC0 of 13 at level 22.
- 4
  Apply any THAC0 modifications due to external effects before rolling the dice. Common modifications are due to spell effects that alter vision, or strength or magic items and weapons carried by the character. For each + to hit, add 1 to the roll on the dice to determine if the player makes their THAC0 roll, for each negative modification, subtract 1 from the dice.
- 5
  Use Table 39, "Creature THAC0" to determine the base THAC0 of creatures. Find the hit dice of the creature on the table. Hit Dice are listed under creature stats and descriptions in the 2nd Edition AD&D Monster's Handbook. The number listed below the "Hit Dice" column on the table is the creature's THAC0. Some creatures have modified hit dice due to special circumstances, such as leadership or champion roles. Often this modification includes additional dice added to the normal creature rates. Add one additional hit dice to the monster's THAC0 on the table if the creature's modification is three dice or more. Modify the listed hit dice as you would the player's THAC0 due to external effects before making your dice roll.

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