Interest rewards you for holding onto cash. At the end of each wave, you earn a percentage of the cash you still have on hand, so money you don't spend keeps working for you. It sits in the Workshop Upgrades category and is supported by two related lab researches.
Overview
Interest pays out a percentage of your unspent cash when a wave ends. The larger the balance you carry into the end of a wave, the more interest you collect, which encourages saving rather than spending everything immediately.
Workshop
Interest/Wave is bought in the workshop for 5000 coins once Free Upgrades is unlocked. It has 99 levels starting from a 0% base, and each level adds 0.06% to that base, reaching a maximum of 5.94%. The payout is worked out after Cash Per Wave is applied, using the formula: (Current Cash + Cash/Wave × Cash Bonus) × Interest/Wave %.
Cost
The cost of each Interest/Wave workshop level is listed in the cost table below.
| Level | Value | Coin | Total Coins |
|---|---|---|---|
| 1 | 0.06% | 125 | 125 |
| 2 | 0.12% | 179 | 304 |
| 3 | 0.18% | 245 | 549 |
| 4 | 0.24% | 328 | 877 |
| 5 | 0.30% | 431 | 1.31K |
| 6 | 0.36% | 556 | 1.86K |
| 7 | 0.42% | 705 | 2.57K |
| 8 | 0.48% | 881 | 3.45K |
| 9 | 0.54% | 1.08K | 4.53K |
| 10 | 0.60% | 1.32K | 5.85K |
Labs — Interest
The Interest lab raises how much each Interest/Wave workshop level adds and also lifts the workshop's maximum value. It has 99 levels, with the per-level values shown in the table below.
| Level | Time | Cost | Value |
|---|---|---|---|
| 1 | 0d 0h 0m | 50 | 1.02 |
| 2 | 0d 0h 10m | 93 | 1.04 |
| 3 | 0d 0h 24m | 221 | 1.06 |
| 4 | 0d 0h 46m | 532 | 1.08 |
| 5 | 0d 1h 17m | 1,126 | 1.10 |
| 6 | 0d 1h 59m | 2,109 | 1.12 |
| 7 | 0d 2h 53m | 3,589 | 1.14 |
| 8 | 0d 4h 2m | 5,677 | 1.16 |
| 9 | 0d 5h 27m | 8,484 | 1.18 |
| 10 | 0d 7h 9m | 12,126 | 1.20 |
Labs — Max Interest
Max Interest raises the cap on how much interest you can earn, which starts at $50. It has 15 levels. You can tell when you've hit the cap because the $ symbol next to your cash display turns bright green.
| Level | Time | Cost | Value |
|---|---|---|---|
| 1 | 0d 0h 42m | 250 | $100 |
| 2 | 0d 1h 10m | 910 | $200 |
| 3 | 0d 2h 8m | 2,129 | $350 |
| 4 | 0d 4h 33m | 4,856 | $500 |
| 5 | 0d 9h 43m | 10,330 | $700 |
| 6 | 0d 19h 12m | 20,021 | $1,000 |
| 7 | 1d 10h 50m | 35,595 | $1,500 |
| 8 | 2d 10h 44m | 58,900 | $2,000 |
| 9 | 3d 21h 10m | 91,939 | $2,500 |
| 10 | 5d 20h 40m | 136,870 | $3,500 |
Labs
The Interest labs are unlocked in the Labs menu through Milestones, at tier 2 wave 80.