Updated for Town Hall 18 (October 2026).
The Gem Mine is a Builder Base building that produces free Gems on its own, from 2.16 a day at level 1 up to 5.04 a day at level 10. You repair it at Builder Hall 3, it tops out at level 10 with Builder Hall 10, and it holds between 10 and 19 Gems before it stops working, so collecting it every few days is the whole trick.
What the Gem Mine does
Every Builder Base resource building makes Builder Gold or Builder Elixir. The Gem Mine is the odd one out: it slowly fills with Gems, the premium currency you use in both villages. Tap it to move the Gems into your account. Gems have no storage limit, so the only cap that matters is the mine’s own capacity. Once it is full, production stops until you collect.
It does nothing for your attacks or your defense. It is a 3×3 building with modest hitpoints that sits on the map like any other structure. Upgrading it raises its output and capacity, but the mine produces nothing while an upgrade is running.
The Clock Tower speeds up everything with a timer in the Builder Base, and the Gem Mine is included. A level 10 Clock Tower boost adds 4 hours 48 minutes of production, which is almost exactly one extra Gem from a max-level mine.
How to unlock it
When you first land in the Builder Base, the Gem Mine is a ruined, overgrown cave. In that state it behaves like an obstacle: you can’t move it, and attackers ignore it. Upgrade your Builder Hall to level 3 and you can repair it for Builder Elixir. After that it is a normal building you can place anywhere on Stage 1, and you only ever get one.
Repair is optional. If you are short on builders early on, rushing defenses or the Star Laboratory first is a fair call, but the mine is cheap at low levels and starts paying out the moment it is fixed.
Gem Mine levels and stats
Every upgrade is paid in Builder Elixir. Times are base values before any Gold Pass builder discount.
| Level | Builder Hall needed | Gems per day | Capacity | Full after | Hitpoints | Cost (Builder Elixir) | Upgrade time |
|---|---|---|---|---|---|---|---|
| 1 | 3 | 2.16 | 10 | 4d 15h | 300 | 120,000 | 1h |
| 2 | 3 | 2.40 | 11 | 4d 14h | 350 | 180,000 | 2h |
| 3 | 3 | 2.64 | 12 | 4d 13h | 400 | 240,000 | 6h |
| 4 | 4 | 2.88 | 13 | 4d 12h | 450 | 450,000 | 8h |
| 5 | 5 | 3.12 | 14 | 4d 11h | 550 | 1,000,000 | 12h |
| 6 | 6 | 3.36 | 15 | 4d 11h | 650 | 1,500,000 | 1d |
| 7 | 7 | 3.84 | 16 | 4d 4h | 750 | 2,500,000 | 2d |
| 8 | 8 | 4.32 | 17 | 3d 22h | 850 | 3,500,000 | 4d |
| 9 | 9 | 4.80 | 18 | 3d 18h | 1,000 | 4,500,000 | 6d |
| 10 | 10 | 5.04 | 19 | 3d 18h | 1,150 | 5,500,000 | 8d |
The in-game info screen rounds the daily rate down to one decimal, so a max mine shows 5.0 a day.
Is upgrading the Gem Mine worth it?
Early levels pay back fast. The late ones are a long game, because each upgrade switches the mine off for days while the gain per level is small.
- Level 8 to 9: you lose about 26 Gems during the 6-day upgrade (4.32 x 6) and gain 0.48 a day afterwards, so you break even after roughly 54 days.
- Level 9 to 10: you lose about 38 Gems over 8 days (4.80 x 8) and gain only 0.24 a day, so the break-even point is around 160 days.
That math ignores the Builder Elixir cost. Since 2.0, Builder Elixir comes from defenses (paid into your Elixir Cart) and the Star Bonus, and Supercell raised those rewards in March 2025, so for many players the scarcer resource is builder time. The extra Builder Base builder from May 2026 makes that cost lower than it used to be. Still, if you have a defense or the Star Laboratory waiting, those come first. A max Gem Mine collected on time gives you roughly 1,840 Gems a year (5.04 x 365) before Clock Tower boosts.
Where to place it
The Gem Mine is locked to Stage 1, the half of the base built around your Builder Hall; it can’t go on the Stage 2 side with O.T.T.O’s Outpost. It counts toward destruction like every other building, so it can’t be skipped for a three-star.
That makes it useful filler. Put it in a far corner, away from where attackers usually deploy, and slower troops can run out of time walking to it. Keep it outside your walls: inside, it takes up space a defense could use, and it adds almost nothing as a buffer at 1,150 hitpoints.
What changed with Builder Base 2.0
Builder Base 2.0 launched on May 15, 2023 and added Builder Hall 10, which brought Gem Mine level 10. The same update split the base into two stages from Builder Hall 6, and the Gem Mine stayed on Stage 1. Supercell also changed Builder Base gem skip costs to match the Home Village rates at that time. The May 26, 2026 update later added an extra Builder Base builder (it requires all Home Village builders first), which frees up time for low-priority upgrades like this one.
Gem Mine FAQ
How many Gems does the Gem Mine make per day?
From 2.16 at level 1 to 5.04 at level 10. At max level that is about 35 Gems a week if you never let it fill.
What is the Gem Mine’s max level?
Level 10, which needs Builder Hall 10. It holds 19 Gems and fills in about 3 days 18 hours.
How often should I collect it?
Every three days is safe at any level. Levels 1 to 6 take about four and a half days to fill; levels 8 to 10 fill in under four.
Can attackers steal Gems from it?
No. Builder Base battles never take loot from the defender. Destroying the Gem Mine only counts toward the attacker’s destruction percentage.
Sources: Supercell, Builder Base 2.0 patch notes (May 15, 2023); Supercell, Clash Anytime update notes (March 2025); Supercell, May 2026 update notes; in-game data.
