The math
Roblox keeps a 30% Marketplace Fee on game passes and developer products and you receive 70%, rounded down to a whole Robux: floor(80 × 7 ÷ 10) = 56.
Nearby amounts
Both directions, using the same rounding as Roblox.
| Amount | List at this, you get | To get this, list at |
|---|---|---|
| 40 | 28 | 58 |
| 60 | 42 | 86 |
| 72 | 50 | 103 |
| 80 | 56 | 115 |
| 88 | 61 | 126 |
| 100 | 70 | 143 |
| 120 | 84 | 172 |
| 160 | 112 | 229 |
Robux transfer version
As a Robux transfer (10 to 500 per transfer) the recipient gets 72 and the game gets 8. Roblox does not document rounding for odd amounts, so this rounds down.