Is it Cheaper to Fill Your Tank When it is Half Empty?


June 17, 2022

The rising cost of gas is among the top political issues on the mind of many (if not most) Americans and sadly it seems that the politicians in office aren't terribly concerned about realistically fixing that issue and as far as I've seen the ones currently running for office aren't campaigning on fixing the problem either. In fact many politicians have showed that they don't care about fixing this problem, and almost all modern American politicians have proven themselves to be wholly incapable of fixing any problem at all so unfortunately this is something we are going to have to live with at least for the next few years.

So if this is something we will have to live with then we need to learn how to best live with it and I've heard the myth that if you make a habit of filling your tank when it is half empty you will be saving money over always filling it when it is almost completely empty. Of course if you're always filling at half a tank each trip to the gas station will be less painful than ones where you fill your full tank but this strategy doesn't change the amount of gas you use over a long period of time so using data from the last year (found here and graphed below) I put the myth to the test.

The Test

The data shows the average price for a gallon of regular gas each Monday morning from June 7, 2021 to June 6, 2022 during which period of time that price nearly doubled from $2.36 to $4.70. The test I ran simulated a driver with a twenty gallon tank who used ten gallons of gas per week, in one instance the driver would buy 20 gallons of gas every two weeks simulating waiting until the tank is empty to fill up, and in the other instance the driver would buy 10 gallons of gas every week simulating always filling up when the tank is half empty. In both of these scenarios a total of 520 gallons of gas was bought. I picked these numbers because they are comparable to the rate at which I consume gas.

The Results

The strategy in the first instance resulted in a total of $1792.38 being spent on gas over the course of a year while in the second $1782.90 was spent, so a driver who always filled their tank when it was only half empty would have saved $9.48 over that year by doing that rather than waiting till their tank was empty.

Why Fill when You're Half Full?

So do you save money by filling your car when it is half full rather than waiting till it's empty? Yes. But is taking twice as many trips to the gas station really worth saving an extra ten bucks a year? Not really. However there is still value in never letting your tank get anywhere near empty. The scout motto is "Be Prepared" and it is a good one to live by, in some sort of crisis where you need to get somewhere fast you don't want to be delayed by a trip to the gas station. By keeping your tank half full you are always ready to move. This kind of advice can be applied into other areas of life as well because we should strive to always have the energy to help those who need us.