Options Assignment Cost Calculator
See exactly what happens when a short option is assigned — the cash required, the effective cost or sale basis after premium, and the share count.
How it works
Shares = contracts × multiplier · Cash at strike = shares × strike · Put basis = strike − premium · Call sale = strike + premium
Assignment is when the holder of the option you sold exercises it, obligating you to transact at the strike. A short put assignment forces you to buy shares at the strike using cash you must have available; the premium you already collected lowers your effective cost basis. A short call assignment forces you to deliver (sell) shares at the strike; the premium raises your effective sale price. Assignment can happen any time before expiration for American-style options, most commonly when the option is deep in the money or around an ex-dividend date.
Worked example
Two short $50 puts (200 shares) with $1.50 of premium collected: if assigned, you pay 200 × $50 = $10,000 for the shares, but with $300 of premium already in hand your net cost basis is $50 − $1.50 = $48.50 per share.
Frequently asked questions
When am I most likely to be assigned?
Assignment risk rises as an option moves deeper in the money and as expiration nears. Short calls face extra early-assignment risk just before an ex-dividend date, when the dividend makes exercising worthwhile for the holder.
Does the premium reduce my loss?
Yes. Because you kept the premium, it lowers the effective price you paid on an assigned put or raises the effective price you received on an assigned call, cushioning the transaction compared with the raw strike.
What if I don't have the cash or shares?
If a put is assigned and you lack the cash, the purchase is typically funded on margin, incurring interest; if a call is assigned and you lack the shares, you are left short and must buy them back. Either can trigger a margin call.
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Educational estimate, not investment advice. Options and margin involve substantial risk.