Run it half as much in winter. Maybe less.

About 8 hours a day in summer, maybe 4 in winter. Maybe less.

The pump’s job is to circulate water and keep stuff from growing. In summer, heat and sunlight mean algae want to party. You need enough turnover to filter the whole pool once or twice a day. A standard residential pool usually needs 8–10 hours in peak season.

In winter, everything slows down. Cooler water means less algae, and if you’re not swimming, you don’t need as much circulation. 4 hours a day is plenty to keep the water moving and prevent stagnant spots. If you live where it freezes, you actually want to run it more in short bursts to keep pipes from icing — but that’s a different problem. For most people, cutting summer runtime in half works fine.

Check your pump’s flow rate and your pool’s volume for exact math, but this is the rule of thumb that has never steered me wrong.