A covered call sells a call against 100 shares you already own. The premium is yours immediately; in exchange you agree to sell the shares at the strike if the stock rises through it. This screener shows the premium beside the upside being given up, because those two numbers are the whole trade and quoting only the first one is how covered calls get mis-sold.
Writing a call against 100 shares converts part of a stock position into income. If the stock stays below the strike, the call expires worthless and the premium is kept. If it rises above the strike, the shares are called away at that price — you keep the premium and the gain up to the strike, and give up everything above it.
That ceiling is the real cost, and it only hurts when you are right about the stock. A covered call is a trade that performs best in a flat-to-mildly-rising market and worst in exactly the rally you were holding the shares for.
A covered call has two outcomes worth quoting separately. The static return assumes the stock is unchanged at expiry: the premium over the cost of the shares. The assigned return assumes the stock finishes above the strike: the premium plus the move from your cost basis to the strike.
Screeners that advertise a single large percentage are usually quoting one of these without saying which. Both are shown here, because a strike that pays well if unchanged and a strike that pays well if assigned are rarely the same strike.
You sell them at the strike price and keep the premium. That is a profitable outcome in nearly every case — it only feels like a loss if the stock ran far past the strike, because you gave up everything above it. Choosing a strike is choosing how much of a rally you are willing to miss.
Yes, through the shares. The premium cushions a decline but does not prevent one: if the stock falls, you hold a losing position with slightly less loss than if you had held it uncovered. A covered call reduces downside a little and caps upside a lot.
That is the trade-off the screener exists to make visible rather than a rule. A closer strike pays more premium and is more likely to be assigned; a further one pays less and leaves more room to run. The table shows both returns so the choice is made with the numbers in front of you.