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Use the original compatible contracts
The position holds a call and writes a put, both strike 100, same underlying, expiry and quantity. The fictional call premium is 6 and put premium 4, so the option pair costs a net 2.
Check both strike regions
Above strike, the call pays S−100 and the put writer owes zero. Below strike, the call pays zero and the put writer owes −(100−S)=S−100. The same linear expression holds on both sides.
Keep payoff and cost separate
| Terminal price | Combined payoff | Simple profit |
|---|---|---|
| 0 | -100 | -102 |
| 80 | -20 | -22 |
| 100 | 0 | -2 |
| 102 | 2 | 0 |
| 120 | 20 | 18 |
Do not erase the initiation record
The pair’s terminal payoff has the shape of a strike-100 long forward settlement. Its supplied premium cash flow is still −2. A complete comparison with an actual forward needs compatible current terms and funding, rather than assuming payoff shape alone makes initial costs equal.