Healing Amplification

Overview
Healing Amplification increases the hit points cured by healing spells and effects. It stacks with various spellpower bonuses. It comes from race, class, items, and miscellaneous sources.

Stacking with Spellpower
Healing Amplification stacks multiplicatively with effects that increase the power of healing spells, such as metamagic feats (e.g. Empower Healing), class enhancements (e.g. Cleric Life Magic), item enchantments (e.g. Devotion), scroll mastery enhancement, etc. Incoming healing is simply multiplied by character's total healing amplification. This multiplication is applied only after rounding the amount after applying spellpower (always rounded down) and is then rounded again (always down too).

Example: Cure Light Wounds on CL 5+ with 20 spellpower and 10% healing amplification should in theory heal: 1.1*1.2*(1d6+7) = 10.56-17.16 rounded to 10-17 Instead it heals: 1.2*(1d6+7) = 9.6-15.6 rounded to 9-15 -> 1.1*(9-15) = 9.9-16.5 rounded to 9-16 Note: The range is discrete with only 6 objects in each set, so the average isn't the average of minimum and maximum.

Racial bonus
Most races don't have racial bonuses to healing amplification, i.e. their racial multiplier is 1.
 * Human Improved Recovery has three stacking tiers of 10% each for a maximum multiplier of 1.331 (available to Humans and Purple Dragon Knights)
 * Half-elves can take two tiers of Human Improved Recovery for a maximum multiplier of 1.21.
 * Warforged start at 0.5 and can take Healer's Friend enhancements three stacking tiers of 10 each (10/20/30) increasing racial multiplier to 0.80.
 * Docent of Blood is an item, but stacks differently than most items. Its 0.1 (10%) is added to Warforged racial heal amp, for a total of 0.90 (when Healer's Friend is maxed)
 * Bladeforged start at 0.4 (or 0.45) and can take enhancements, increasing racial multiplier to 0.70.

Class bonus
Class bonuses from different classes stack (are multiplied).
 * Monks get 5% heal amplification per each core ability of the Shintao tree.
 * Half-Elf Monk Dilettante enhancements (Half-Elf Improved Recovery) has two stacking tiers each for a maximum multiplier of 1.21. (This is a class bonus, stacks with racial, locks out monk's amplification)
 * Paladins can get 3x 10% heal amplification enhancements in the Knight of the Chalice tree.

Item bonus
The healing amplification item enhancement comes in three levels (10/20/30 %). Items with the same level do not stack. Items with various levels of healing amplification stack. The bonuses are multiplied, for a total of 1.1 * 1.2 * 1.3 = 1.716. (71.6% total amplification)

Healing amplification 10%
 * Dragontouched Armor, Eldritch
 * Greensteel Weapon - Tier 1
 * Lesser Convalescent random loot
 * Vengeful Protector

Healing amplification 20%
 * Tira's Splendor rune arm
 * Convalescent random loot
 * Dragontouched Armor, Tempest
 * Greensteel Weapon - Tier 2
 * Levik's Bracers (From Hound of Xoriat raid)
 * Can be crafted on Tower of Despair Rings (Incredible Potential)
 * Epic Bejeweled Letter Opener
 * Wall of Wood (Level 22)

Healing amplification 30%
 * Greater Convalescent random loot
 * Greensteel Weapon - Tier 3
 * Epic Gloves of the Claw
 * Purple Dragon Gauntlets
 * Wall of Wood (Level 23)

Miscellaneous bonus

 * Paladin Passive Past Life Feat (stacks additionally 3 times, for a total of 5%, 10% or 15%)
 * Jidz-Tet'ka - +25% insight bonus for Monks in fire stance.
 * House Jorasco Healer Contract from Guild Airships (10 %)

Fleshmaker
The Fleshmaker item enchantment adding 10% has a unique mechanics and stacks in a different way. For best effect, equip the Fleshmaker item first and then add other sources of healing amplification. In most cases the net result will be slightly over 10%, and as high as ~17% if you equip all three tiers of standard healing amp after your fleshmaker item.

healed hp = base heal amount * heal amp +  base heal amount * heal amp sources equipped after fleshmaker * 0.1 (fleshmaker)

For example, when you equip heal amp 10 %, fleshmaker, and heal amp 20% and use a heal scroll:

healed hp = 110 * 1.1 * 1.2 +  110 * 1.1 * 0.1 = 145 + 12 = 157 (If fleshmaker gave only 10%, the expected value would be 156.) (If it stacked like healing amplification items, the expected value would be 110 * 1.1 * 1.2 * 1.1 = 159.)


 * Healing Amplification guide by vyvy3369, explains the unusual way Fleshmaker works