Gym Combat Mechanics

For a more general overview, please check out the Gym Overview and Strategy Guide!
Overview

Unlike in the original series, Pokemon GO gyms are under partial user control. Members of the team that is in control of a gym can assign their own Pokemon to help defend the gym, but they cannot actually control their Pokemon in combat. This design choice leads to some peculiarities with the gym combat system:

  • There are different mechanics for attacking opposing gyms compared to training friendly gyms.
  • In battle, attacking Pokemon (attackers) and defending Pokemon (defenders) have different mechanics.
Differences Between Attacking and Training Gyms

The biggest difference between attacking an opposing gym versus training at a friendly gym is attackers can team up in a fight, up to twenty trainers at once. No defending Pokemon is invincible when ganged up by multiple attackers. As a result, attacking is much easier than training when you have teammates with you.

Prestige calculation is also different for attacking and training. When attacking a rival gym:

Mechanic Prestige XP
Each defeated Pokemon -1000 100
Full Clear bonus -1000 50

When training, if defending Pokemon's level is higher than the trainer, it'll be scaled down to match. Prestige and experience gain depend on Attacker CP (A) and Defender CP (D), with following rules:

CP Ratio Prestige XP
Attacker ≤ Defender 500 * D/A
(1,000 max)
50 * D/A
(100 XP max)
Attacker > Defender
310 * D/A - 55
(100 min)
31 * D/A - 5
(10 XP min)

  • If Defender CP has been scaled down, use the scaled down CP.
  • Use Ditto's post-transform CP for both attacking and defending Ditto (see Ditto Mechanics for more info).
  • Attacking CP used is always highest in the attacking lineup.

Gym attacking is faster than gym training. Outside of specialized strategies such as Bubblestrat, it's more rewarding to attack an opposing gym than training a friendly one.

Attacker and Defender Battle Mechanics

After assigning a Pokemon to a gym, trainers no longer retain control of that Pokemon until it's knocked out from the gym. Instead, the defending Pokemon is controlled by a rudimentary AI in battle.

Player-controlled attackers and AI-controlled defenders fight under a different set of rules:

MechanicsAttacking TrainerGym Defense AI
Lineup Up to 6, in order of trainer's choice Up to 10, in order of increasing CP
Maximum HP Unchanged Doubled
Energy capacity 100 100
Initial attack At 99.3 seconds on the game clock At 98.4 seconds on the game clock
Quick move duration Unchanged +1.5~2.5 seconds
Charge move duration Unchanged +1.5~2.5 seconds
Charge move usage At attacker's discretion 50% chance when energy is sufficient
Energy gain per HP lost -2 HP = +1 energy -2 HP = +1 energy
Effectively doubled due to 2x HP
Switching Yes, 1 second cooldown No
Dodging Yes, 0.5 second cooldown No

While attackers benefit from using high-DPS quick moves, defenders benefit more from using slower, heavier-hitting quick moves. The doubling of defender HP also encourages choosing defending Pokemon with a higher HP stat.

These mechanical differences mean that defenders deal less damage, but they can also tank more damage in battle. The defender can also potentially use more charge moves, since over a round of battle, they will be gaining more energy from damage received. The defender effectively has access to another HP bar's worth of energy in a full battle. This can have devastating consequences, such as a defending Snorlax being able to fire off 3 Hyper Beams in one round of battle.

Dodging

For details on how damage is calculated, see Damage Mechanics.

Attacking Pokemon can attempt to dodge incoming attacks. A successful dodge reduces damage received by 75%:

$$Dodge Damage = max(1, floor( ¼ Damage))$$

To successfully dodge, the attacking player must swipe left or right across the screen after the yellow flash of the defender's attack animation. Our video analysis indicates this dodge window closes 700ms from the yellow flash regardless of the attack. All that matters is the yellow flash.

See our guide on dodging for details

Switching

When attacking an opposing gym, the attacking trainer may choose up to 6 Pokemon to place in his lineup. When a Pokemon faints, it is automatically switched out to the next Pokemon in the lineup, from left to right, top row to bottom row.

The attacking trainer can also opt to switch out Pokemon mid-battle, perhaps to leverage a more favorable type matchup or to prevent a Pokemon from fainting.

In Summary

Gym battles generally favor the attacker for the following reasons:

  • In a prestige race, gym mechanics favor attacking over training a friendly gym (except when using the Bubblestrat).
  • In battle, the attackers typically output higher DPS compared to defenders.
  • The attacking trainer can dodge, which results in a 75% damage reduction.
  • The attacking trainer can select his 6-Pokemon lineup to leverage advantageous type matchups. He can also switch Pokemon mid-battle.

Gyms in Pokemon GO are designed to be easy to attack and difficult to defend, but understanding these gym mechanics and studying the gym defenders tier list can help bolster your chances at a successful defense.

Quick Links
Tools

Pokemon List

IV Calculator

Moves List

Appraisals

Egg Chart

Type Chart

Power Up Costs

Buddy Distances

CP Calculator
Rankings

Gym Attackers

Gym Defenders

DPS per type