Delta 50

Subtype of ATM Def

The fx option is considered to be at-the-money when its strike K is such that call delta = |put delta| = 0.50, with the prices being calculated using the Black Scholes formula
Black Scholes FX formula
This definition applies only when the delta is defined as in
Fwd

The strike K will be as follows:
K = fe½σ²τ
Web reference available
here