A stock's price is expected to drop by roughly the dividend on the ex-dividend date, and option prices embed that drop in advance: calls on dividend payers price lower and puts higher. The sharpest practical effect is early assignment risk on short in-the-money calls the day before ex-dividend, when the dividend exceeds the call's remaining time value.
Through the forward price: an option is a claim on the stock's future price, and known dividends reduce that expected future price without being a loss to a shareholder. Pricing models carry this as a dividend yield or a discrete dividend stream. Ignoring it biases everything downstream: calls on payers read slightly too cheap, puts slightly too rich, and implied volatilities solved without the dividend inherit the error, worth up to a few volatility points near large ex-dividend dates. This is why careful pricing engines, including the one behind Options Scanner's greeks, feed dividend yields into the math rather than assuming zero.
The holder of an in-the-money call faces clean arithmetic the night before ex-dividend: exercise, own the stock, and collect the dividend, or hold the call and skip it. Exercising forfeits the call's remaining time value, so the rational holder exercises exactly when the dividend is larger than that remaining time value, which is common for deep in-the-money calls close to expiration. The short side of that call should therefore expect assignment in that configuration, and a covered-call or spread workflow checks the comparison, dividend versus the short call's time value, as each ex-dividend date approaches. Assignment there is not a malfunction; it is the other party taking the better side of a known trade-off.
Three dates and one comparison: upcoming ex-dividend dates for every name with short calls in the book, the size of each dividend against the short call's remaining time value, and, for wheel-style positions, whether an assignment just before ex-dividend actually hurts (early assignment on a covered call near the cost-basis floor mostly accelerates the designed outcome, minus the dividend). Screens that already gate on earnings dates extend naturally to ex-dividend dates; both are calendar events that change the statistics mid-trade.