Break-even is the underlying price at which your option would be worth exactly what you paid at expiration. For a long call it's the strike plus the premium; for a long put it's the strike minus the premium.

The formulas

Long call break-even = strike + premium paid. Buy the SPY 741 call for $1.20 and, held to expiration, you break even at 742.20 — SPY has to clear the strike and pay back your premium.
Long put break-even = strike − premium paid. Buy the 739 put for $1.00 and you break even at 738.00.

Why scalpers profit long before break-even

That formula assumes you hold to expiration, when only intrinsic value remains. A scalper almost never does. Intraday, your option still carries extrinsic (time) value, so a favorable move makes you money well before price reaches the expiration break-even. If you buy the 741 call and SPY jumps to 741.50 in ten minutes, you're likely green — even though the “break-even” is 742.20 — because the option still holds time value.

Break-even is where a holder profits. A scalper is a renter of time value — you're out long before the clock forces the question.

The trap

The danger runs the other way too: as expiration nears, that time-value cushion evaporates (theta), and the expiration break-even becomes very real very fast. An option that was green mid-morning can need SPY to actually clear break-even by mid-afternoon. Know both numbers — the intraday reality and the expiration line — and don't let a winning scalp turn into a hold that has to reach break-even to survive.