options spread max loss and gain

for selling spread options

Maximum gain = net credit, realized when both options expire

Maximum loss = difference in strike prices - net credit.

For example,
Mini HSI index bull put spread
buy put 22000 $35 $350
sell put 22400 $70 $700
max gain = $700 - $350 = $350
Max loss = $4000 - $350 =$3650