Hit chance

Hit chance is a calculated statistic that determines whether or not an attack will land. In its simplest form, hit chance is simply a function of accuracy, armour, and affinity; however, various modifiers (such as equipment or Buffs) can change hit chance.

When discussing changes to hit chance, modifiers are either additive (directly affecting hit chance) or multiplicative (affecting one of its variables). Additive bonuses are added directly the final calculation, whereas multiplicative bonuses modify a variable in the calculation. In this sense, accuracy is distinct from hit chance; the latter being a function of the former.

The PvE hit chance formula
In player-versus-monster combat, one's hit chance is the chance of successfully hitting a monster (or the chance of a monster hitting you), given your accuracy, the armour of your opponent and the style you are using.

Your hit chance $$H$$ (as a percentage) is calculated as:
 * $$H = Aff \times \Bigg( \frac{a}{d} \Bigg )$$

Where:
 * $$Aff$$ is affinity
 * $$a$$ is your accuracy
 * $$d$$ is the target's armour rating. Generally, this is the sum of their armour and armour bonus granted by their defence level.

Affinity
Depending on what style you're using and what type of monster your target is, the Affinity variable can be one of 4 values. By default those values are:
 * 90 when using the target's specific weakness. (eg. arrows, bolts, slash, stab, air, fire, etc.)
 * 65 when using a combat style the target is weak against, but not the specific weakness (eg. melee against a ranger)
 * 55 when using a combat style the target is neutral against (eg. melee against a meleer)
 * 45 when using a combat style the target is strong against (eg. melee against a mage)

Generic weaknesses to melee, ranged or magic will use the respective melee, ranged and magic affinity value rather than the weakness affinity value.

Some NPCs have custom set values for each affinity. For example, some bosses have 40 on all affinity values.

Calculating accuracy
There is a single formula that relates level to accuracy bonus for base levels, weapons and monsters. Given a as the level, the formula is: $$F(a) = 0.0008a^3 + 4a + 40$$

For simplicity this formula will be referred to as F, so for example F(99) would be 1212.2, which rounds to the true value of 1212 (the level accuracy bonus of a player with level 99 Attack).

Note that drinking potions and using stat-boosting prayers will increase the input value for this.
 * Using a supreme overload boosts your attack level by 16% +4, or to 118 at 99. F(118) would be a 1826 accuracy bonus.
 * Using turmoil invisibly boosts your attack level by 10. At level 99, this boosts it to 109. F(109) would be a 1512 accuracy bonus.
 * Using both a supreme overload and turmoil brings your attack level to 128. F(128) would be a 2230 accuracy bonus.

Your base accuracy
$$accuracy = F(a)+ 2.5 \times F(weapon)$$

Your accuracy is given by your level accuracy bonus added to your weapon's accuracy bonus. The level accuracy bonus is F(attacklevel) and the weapon accuracy bonus is 2.5 * F(weapon level). Therefore a player with 99 Attack using Drygore weaponry would have F(99) + 2.5 * F(90) = 3670 accuracy.

Equipment penalty
Wearing armour of the wrong class, excluding hybrid class, will negatively impact hit chance. Affected item slots include the helm, body, legs, boots, gloves, and shield slot. Depending on the weapon type, wearing armour from the class you are strong against (ie. if using Melee, this is Ranged) will result in an accuracy penalty that is 3/2 (x1.5) the item's armour stat. Wearing armour of the class you are weak against (if using Melee, this is Magic) will result in an accuracy penalty that is 4/5 (x0.8) of that item's armour stat. This penalty is reinforce the combat triangle system and to prevent players from abusing the combat triangle weaknesses.

Accuracy boosts
There are various things that can be used to increase your accuracy rating; these simply multiply your accuracy value by a number, and can be stacked with one another. These include:

Hit chance boosts
Also known as flat or additive accuracy bonuses. Unlike the above mentioned accuracy bonuses; these add the value directly to your final hit chance, rather than multiplying it. These can also be stacked with one another.

An example to better distinguish between both types: If you have 60% hit chance, then a 10% accuracy bonus multiplies it by 1.1, thus becoming 66% hit chance. A 10% hit chance bonus adds 10% to 60% thus becoming 70% hit chance.

This means that hit chance bonuses are superior to equal numbered accuracy bonuses

Hit Chance Examples
Using Saradomin godsword (slash style) at Abyssal demon (slash weakness) with 99 attack: hit chance is capped at 100%, so all attacks will not miss.
 * $$Aff=90$$
 * $$a=F(99)+2.5*F(75)=2906$$
 * $$d=1608+F(70)=2202$$
 * $$H=Aff \times a/d=118.8%$$

On the other hand, using Sunspear (ranged) with 99 ranged in void knight armour will result in misses:
 * $$Aff=45$$
 * $$a=F(99)+2.5*F(78)=3041$$
 * $$d=1608+F(70)=2202$$
 * $$H=1.03 \times Aff \times a/d=64.0%$$

For a Queen Black Dragon bossing situation, using Royal crossbow, Overload, Anguish, and Royal bolts with 99 ranged will result in misses:
 * $$Aff=50$$
 * $$a=F(126)+2.5*F(80)=4068$$
 * $$d=2075+F(80)=2845$$
 * $$H=Aff \times a/d=71.5%$$

Swapping for Dragonbane arrow will provide an additive bonus to hit chance: and therefore reaching hit cap.
 * $$H=Aff \times a/d + 30=101.5%$$

Boss armour ratings
The tables below are for quick look-up of the total armour rating of current bosses. For the affinity values to your combat style, refer to the boss's individual page.

God Wars Dungeon 1
Bosses include: Commander Zilyana, General Graardor, Kree'arra, K'ril Tsutsaroth, and Nex.

God Wars Dungeon 2
CM refers to challenge mode. Note: The stats shown for Vindicta are for her second phase which are higher than the first.