Senja Fitz

I have purchased shares through my US employers ESPP program where the gain has been added to my ordinary income at each event and taxed. I'm planning to sell them all this year but wanted to clarify the gain calculation for the self assessment. Example: the market value was 50,000 and I paid 45,000 with the 5,000 taxed as ordinary income. I'm selling them for 60,000. Is the gain calculated as 1) selling price - market value (50,000) OR 2) selling price - price paid (45,000)?