Tower Defense Economy Guide: Earn, Spend and Save Smarter
Towers win games, but gold decides which towers you get and when. Two players with the same strategy can have very different results depending on how efficiently they turn income into damage. This guide explains exactly how the economy works in our games and gives you a framework for spending decisions.
The same rules apply across all fifteen games, with one notable exception in Endless Defense. Where a game uses a themed currency, the rules are identical: Energy in Space Defense and Robot Defense, Supplies in Zombie Defense.
Where your gold comes from
There are two income sources in every game:
- Kill income: gold for every enemy defeated.
- Wave-clear bonus: a payment when you finish a wave.
Endless Defense adds a third: 5 % interest on banked gold at the end of each wave, capped at 50 per wave.
Because income comes from kills, a stronger defence earns more. Every enemy that leaks is gold you did not collect, on top of the lives you lost. Early efficiency compounds: a good first few waves put you ahead for the rest of the game.
What spending really costs
Selling refunds 70 %
When you sell a tower you get back 70 % of everything spent on it, including upgrades. So moving a tower costs you 30 % of its total investment. A heavily upgraded tower in the wrong place is expensive to relocate, which is why placement deserves care before you start upgrading.
Selling is still a legitimate tool. Late in a game, selling a tower that no longer contributes (for example, an early cheap tower covering a stretch enemies now pass untouched) and putting the refund into an upgrade where the action is can be worth the 30 % loss.
Upgrades
Every tower has three levels; level 1 is what you build, and the upgrade cost is shown on the button. Robot Defense adds a fourth level with a choice of two specialisation branches. Upgrades keep your investment on a tile you already know is good, and bigger hits are more efficient against armor, which reduces every hit by a flat amount. Read how tower upgrades work for more.
New tower or upgrade?
This is the central economic decision. There is no single answer, but these rules of thumb work well:
| Situation | Usually better | Why |
|---|---|---|
| A route or lane has little or no coverage | New tower | Coverage gaps cause leaks no upgrade can fix |
| Armored enemies are surviving | Upgrade a heavy hitter | Bigger hits lose less to flat armor |
| Swarms are leaking | New splash tower | Splash hits every enemy in the blast radius |
| Enemies move too fast through the zone | One slow tower | Slows do not stack, so one is enough per zone |
| You have a cluster of damage towers | A support tower | Boosts every tower in its radius (only the strongest boost applies) |
Support towers such as the Amplifier in Endless Defense or the Radar in Desert Defense can be excellent value because they multiply damage you already paid for, but only if several towers sit inside the radius. A second support covering the same towers adds nothing, since boosts do not stack.
Spend before you start the wave
Outside Endless Defense, gold in the bank earns nothing. Unless you are saving for a specific upgrade you will buy after the next wave, spend what you have during the build phase. Enemies in the next wave do not care how much gold you are holding.
Interest in Endless Defense
In Endless Defense, interest changes the calculation. Because the payment is 5 % of banked gold and capped at 50 per wave, the cap is reached at 1,000 banked gold. Holding more than that earns no extra interest, so it is just unused money.
A practical approach:
- In early waves, when enemies are weak, let your bank build toward the cap while spending enough to kill everything.
- Once you are at or near the cap, spend anything above it.
- If a wave looks dangerous, spend into the bank. Interest is not worth losing lives, and health scales every wave so falling behind is hard to recover from.
Our endless tower defense strategy guide covers long-run planning in more depth.
Cheap tools with high value
Some purchases are worth far more than they cost. In Maze Defense, the Wall is cheap and has no attack, but it lengthens the route enemies must walk past your damage towers. A few walls that double the time enemies spend in range can be worth more than another attacking tower. Walls are also cheap to sell and move if your maze needs changing.
Economy under tight budgets
The Daily Tower Defense Challenge sometimes uses a low-gold rule, and it always sets its own starting gold. With a tight budget:
- Build fewer towers in the single best spot rather than covering everything.
- Avoid selling; the 30 % loss hurts more when every coin matters.
- Prefer upgrades on proven towers once coverage is adequate.
- Kill everything: each leak also costs you the kill income.
Summary
- Income comes from kills and wave-clear bonuses, so a good defence pays for itself.
- Selling costs 30 % of the investment; place carefully before upgrading.
- Spend before each wave, except when banking toward the 1,000-gold interest cap in Endless Defense.
- Choose between new towers and upgrades based on what is actually leaking.
For the broader picture, read our guide to resource management in tower defense.
