Gasoline costs add up. Saving a few cents a gallon by avoiding midweek fill-ups could translate to hundreds of dollars per year. The cheapest gasoline prices of the week are usually on Sunday, though the cost may stay low on Monday before rising midweek. Read on for the details and how this cycle varies by state.

The GasBuddy app and website have been updating gasoline prices daily for 25 years. This gives it a useful set of data. Patrick De Haan, head of petroleum analysis, explained, “Gas prices don’t just move based on global oil markets — they also follow a weekly rhythm.”

Luckily for us penny-pinchers. This weekly rhythm is shockingly predictable. And knowing it could save you 9 cents a gallon. Prices rise through the week, then ease into the weekend, bottoming out on Sunday, before rising again on Tuesday. “For most drivers, Sunday is the safest bet for finding lower prices, while filling up mid-week can mean paying more.”

It’s relatively easy to pair topping off your tank with other Sunday errands. And if you join a loyalty program at a store such as Costco or a regional grocery chain, you can enjoy even lower prices at their dedicated pumps. But not every state is the same.

In some places, gas prices “reset” on a specific day, rising sharply. Then they decline slowly over five to seven days. This strategy, known as “price cycling,” is common in Michigan, Indiana, Ohio, Florida, Texas, and parts of the West Coast.  If you see a shocking increase in gasoline prices everywhere on the same day, try to hold out for a week before buying a full tank.