Put-Call Parity states that for European options on a non-dividend-paying stock:

C − P = S − PV(K) = S − Ke-rT

If this relationship is violated, a riskless arbitrage profit exists.

Synthetic Positions

Put-call parity allows creating synthetic positions:

  • Synthetic Long Call: Long put + Long underlying
  • Synthetic Long Put: Long call + Short underlying
  • Synthetic Long Stock: Long call + Short put (same strike)
  • Synthetic Forward: Long call + Short put = long futures (approximately)