Model and input conventions
Both options must share underlying, strike, expiry and premium currency. The model parity value is spot multiplied by exp(−yield × years), minus strike multiplied by exp(−rate × years). Subtract that amount from the observed call premium minus put premium. Rates use continuous annual compounding, percentage entries are divided by 100, and years equal calendar days divided by 365.
Worked numerical example
Take spot and strike of 100, one year remaining, zero yield and a 5% rate. The discounted parity value is approximately 4.877058. A call premium of 12.450584 paired with a put premium of 5.573526 produces a discrepancy of approximately +2. With a combined per-unit cost allowance of 0.50, the absolute residual allowance is 1.50; reversing which premium is elevated reverses the discrepancy sign.
Read the scenario table
The table separates the two observed premiums from the discounted spot and strike components so unit mistakes can be traced directly. The matching-call and matching-put metrics answer what one quote would need to be for this exact parity equation to balance. They do not price early exercise or independently estimate volatility. Recalculate whenever either quote, expiry distance or funding assumption changes.
Where the model stops
Real execution requires the correct bid or ask on every component, borrowing and lending access, compatible settlement and available short inventory. A midpoint gap does not establish those conditions. Fees entered here are a single allowance and do not reconstruct financing cash flows. Unexpected negative implied matching premiums usually warrant checking inputs before interpreting the result as a market inconsistency.