The formula
A pad's payback time is its purchase cost divided by its income rate:payback (seconds) = cost (cash) ÷ income (cash/s)Once a unit repays its cost, everything it earns is profit — which is why income rate, not the rarity label, is the number that matters. The confirmed Secrets span 2.3M to 225M cash/s despite all sharing one rarity, so two pads with the same tag can differ by almost 100x.
Worked example from documented values
Los Tictacs cost 15B cash and earn 60M cash/s, so 15,000,000,000 ÷ 60,000,000 = 250 seconds — about four minutes of pad uptime. Moby Bros at 225B ÷ 225M/s = 1,000 seconds, about seventeen minutes. Those are ideal cases: the cash piles up in your collect zone until you walk through it, a thief can take the unit plus the pile the moment your door unlocks, and every slap or trap on the carry home is time at zero income.