Preservation Chance

Preservation Chance is a modifier which allows resources to be preserved when creating items, allowing for the creation of items at no cost to the player. When resource preservation triggers, the player will receive a notification stating "You managed to preserve your resources".

The generic "chance to preserve resources" only applies when creating items within a skill, it does not affect:

Potion charge preservation
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Summoning tablet preservation
Prayer point preservation
Rune Preservation in
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Magic
Ammo Preservation in
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Ranged
Dig site map excavation preservation in
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Archaeology

The preservation chance for all skills is capped at 80%, unless a modifier which increases the cap applies.

Like preservation, doubling helps create more output for the same input. But doubling does this by increasing the output for each action taken, while preservation increases the number of actions possible for each unit of input. For sources of doubling, see Skill Boosts#Doubling Boosts for global modifiers or the "Skill Boosts" section of a specific skill. See Double Loot for more about doubling in combat.

Chance Cap

The preservation chance for all skills is capped at 80%. For a few skills, there exists bonuses which can increase this cap:

The
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Bear & Beaver synergy can increase the cap for
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Fletching by 5%
The
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Bear & Fox synergy can increase the cap for
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Herblore by 5%
The Herblore Preservation Scroll from
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Township can increase the cap for
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Herblore by 5%. This stacks with the above.

Calculating Gains

Let's say you have 120 bars, 80% resource preservation, and 0% doubling chance. If a dagger takes one bar to create, how many daggers would you create on average out of 120 bars?

The answer is [math]\displaystyle{ \frac{120}{1 - 80/100} = \frac{120}{0.2} = 600. }[/math]

The main idea behind resource preservation is that you can reuse the preserved resources to make more items, but those resources when used will themselves be preserved also.

Using the same example with 120 bars, you take 120 actions producing 120 daggers, but with 80% preservation you are left with [math]\displaystyle{ 120 \times 0.8 = 96 }[/math] bars.

Now you can use those 96 bars to do the same thing, and you will be left with [math]\displaystyle{ 96 \times 0.8 = 76.8 }[/math] bars on average.

Repeat that to infinity, and you will get the average number of daggers that you will produce from 120 bars.

But how do we calculate this number?

So the number of daggers produced is [math]\displaystyle{ 120 + (120 \times 0.8) + (120 \times 0.8 \times 0.8) +\cdots + (120 \times 0.8^n) }[/math] where [math]\displaystyle{ n }[/math] goes to infinity.

If we generalize and represent the number of starting resources ([math]\displaystyle{ 120 }[/math]) with [math]\displaystyle{ a }[/math] and the probability ([math]\displaystyle{ 0.8 }[/math]) with [math]\displaystyle{ r }[/math], the number of actions performed with [math]\displaystyle{ a }[/math] action's worth of starting resources and a resource preservation of [math]\displaystyle{ r }[/math] (where [math]\displaystyle{ 0 \le r \lt 1 }[/math]) can be expressed as follows:

[math]\displaystyle{ a + (a \times r) + (a \times r \times r) + \cdots + (a \times r^n) = \sum\limits^{\infty}_{n=0} ar^n }[/math]

This expression is an infinite geometric series, which can simply be expressed as [math]\displaystyle{ \displaystyle \lim_{n \to \infty}\tfrac{a(1 - r^n)}{1 - r} = \frac{a}{1 - r} }[/math].

So, coming back to our example where [math]\displaystyle{ a = 120 }[/math] and [math]\displaystyle{ r = 0.8 }[/math], we get [math]\displaystyle{ \frac{120}{1 - 0.8} = 600 }[/math].

Sources

For a list of boosts that apply to all skills, see the Skill Boosts page.

Skill	Page
Error creating thumbnail: File missing Ranged	Ranged/Boosts#Preservation Boosts
Error creating thumbnail: File missing Magic	Magic/Boosts#Preservation Boosts
Error creating thumbnail: File missing Prayer	Prayer/Boosts#Chance_to_Preserve_Prayer_Points Prayer/Boosts#Chance_to_Preserve_Soul_Points
Error creating thumbnail: File missing Farming	Farming/Boosts#Preservation Boosts
Error creating thumbnail: File missing Firemaking	Firemaking/Boosts#Preservation Boosts
Error creating thumbnail: File missing Cooking	Cooking/Boosts#Preservation Boosts
Error creating thumbnail: File missing Runecrafting	Runecrafting/Boosts#Preservation Boosts
Error creating thumbnail: File missing Herblore	Herblore/Boosts#Preservation Boosts
Error creating thumbnail: File missing Summoning	Summoning/Boosts#Preservation Boosts
Error creating thumbnail: File missing Alt. Magic	Alternative Magic/Boosts#Preservation Boosts
Error creating thumbnail: File missing Cartography	Cartography/Boosts#Preservation Boosts