Path of Idle mana guide: the cost curve and how to survive it
Mana cost is a flat number, and it is set by two things: the skill’s cooldown and the skill’s level. A skill with a 15 second cooldown costs 210 mana at skill level 1 and 825 at level 10. Nothing about your mana pool changes those numbers.
That is why maxing every active skill is the most common cause of an empty mana bar, and why lowering a skill by two or three levels often fixes a hero completely.
The cost curve
Mana cost equals a per level factor multiplied by the skill’s cooldown.
| Skill level | Factor | Cost of a 6 second skill | Cost of a 15 second skill |
|---|---|---|---|
| 1 | 14 | 84 | 210 |
| 3 | 22 | 132 | 330 |
| 5 | 31 | 186 | 465 |
| 7 | 40 | 240 | 600 |
| 10 | 55 | 330 | 825 |
Going from level 1 to level 10 multiplies the cost by about 3.9. Long cooldown skills are the expensive ones: Lightning Storm, Light Wind and Slime Rain all sit at 825 or 770 mana when maxed.
The useful reading is that skill level buys damage and costs mana at roughly the same rate, so a hero who cannot sustain their rotation is not gaining anything from the last few levels. Drop the most expensive active skill by two or three levels before you rebuild the whole hero.
Reservations also grow with skill level
Auras and allies do not cost mana per cast. They reserve a percentage of your pool permanently, and that percentage rises as you level the skill.
| Skill | Reserves at level 1 | At level 10 |
|---|---|---|
| Frost Wolf Ally | 40% mana | 53% mana |
| Brilliance Aura | 25% mana | 35% mana |
| Strike Aura | 20% mana | 30% mana |
| Aura of Focus, Flame or Lightning | 25% mana | 35% mana |
| Brown Bear Ally | 35% health | 48% health |
| Killing Aura | 20% health | 30% health |
This is the trap. Levelling an aura for a stronger effect shrinks the pool that everything else draws from. A Hunter running Frost Wolf Ally at level 10 has 47% of their mana left for actual skills.
The Mana Reservation attribute reduces how much reservation effects take, and it uses the diminishing formula rather than subtracting directly. It is the one stat that makes multiple auras affordable.
Note that Killing Aura and Brown Bear Ally reserve health, not mana, which is why a Hunter running both allies looks permanently low on health while being perfectly safe behind shields.
Where mana comes back
Mana Regen is a flat amount restored per second. It is not inherited by allies or minions, so a summoner’s regen is theirs alone.
Mana on Kill restores a set amount per kill. That makes it strong in the campaign, where a level site is 8 enemy groups, and weak against a boss, where a site is one group. If your problem is boss fights specifically, Mana on Kill will not solve it, and the boss wall checklist is the better starting point.
Brilliance Aura is the Mage skill that gives all allies increased Mana Regen and increased Buff Duration. Other jobs can reach it through the Radiance runeword, which is a Mage runeword granting Brilliance Aura. That is the standard way a party without a Mage gets a regen aura, and it costs one Common item slot with three sockets. The runes and runewords guide covers how to build one.
One skill actually generates mana. The Mage’s Lightning Shock has a mana cost of minus 12 at every level, so casting it returns mana instead of spending it. That is a large part of why the Lightning Basic Attack build is rated easy: its damage engine does not compete with its resource bar.
Cost reduction is diminishing
Martial Cost, Spell Cost, Mastery Skill Cost, Utility Skill Cost and Support Skill Cost all reduce the mana cost of skills in their category, and they use the diminishing reduction formula rather than subtracting a flat percentage. Stacking them gives less and less.
They also only apply to their own category. Martial Cost does nothing for a Spell, and a skill that is neither Martial nor Spell uses a runtime default. The combat rate calculator shows exactly what a given combination produces.
The fix list, in order
- Lower your most expensive active skill by two or three levels. Cost falls faster than damage does at the top of the curve.
- Check what your auras and allies reserve. An aura at level 10 can be taking a third of the pool.
- Add Mana Regen if the problem is sustained fights, or Mana on Kill if it is clear speed.
- Get a Brilliance Aura into the party, through a Mage or through the Radiance runeword.
- Add Mana Reservation if you genuinely need multiple auras running.
- Only then start hunting cost reduction affixes, since they diminish.
For which attributes are worth an item slot in general, see which attributes matter.