Cost basis after assignment calculator: what the shares really cost you
You were assigned. The shares cost the strike on paper, but every premium you collected came off that price. Find your real basis per share, your break-even, and how far today's price is from it.
| If you sold at | Result vs. your basis |
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How it works: when a short put is assigned you pay the strike for the shares, but every premium you collected on that stock along the way came off the price. Cost basis per share = strike − all premiums collected. Break-even is that same number: sell above it and you're ahead, below it and you're behind. The gap to today's price is shown in dollars and as the percentage the stock would need to move to get back to your basis. Fees left out. An illustration of the math on your inputs, not a trade idea.
Your broker's screen may show a different number
Many brokers list the strike as what you paid, and show the premium as a separate closed trade. Both views are right; this one just puts them together so you know your real break-even. How the premium is treated for tax differs by country and account type (and in a registered account like a TFSA, RRSP or IRA it may not matter at all), so check with your broker before you rely on either number. What assignment does mechanically is in options assignment, explained.
The basis decides which call to sell next
In the wheel strategy the step after assignment is selling a covered call. The basis is the floor for that strike: a call at or above it means being called away is a small gain or a wash; a call below it means being called away locks in a loss. When the stock has fallen a long way, the honest choices are a call above the basis for a small premium, or waiting — not a fat premium at a strike that locks in a loss if it's hit. Keep adding each new premium to the box above and the basis keeps falling, which is the only thing the wheel can do for a stock that went against you.
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