I love GasBuddy. Especially when out on the road in unfamiliar territory it’s helped me find some great deals by continuing down the road to the next exit, or going slightly off the beaten path, to save a few cents a gallon.
But the other day I was presented with a dilemma. A station three miles out of our way was a cent cheaper than one along our route. I wasn’t running on fumes but I also wasn’t in a position to make it all the way home without gassing up, either. Where should I buy?
In our quest to save a cent here or a cent there, how much money have I potentially been wasting?
Thus, I want a smartphone app called “Is It Worth the Drive?”
The way I imagine it, the app would retrieve data from GasBuddy or a similar service (so ideally it would be written by a company providing that service, or implemented into their existing apps) so it knew all of the prices around your GPS location. You would provide the MPG of your car in the setup phase, so it would be able to calculate (on average) how much gas you would use to get to each station, round trip. (Or, if implemented into turn-by-turn navigation, to get there and continue along your route.) You’d also tell it how many gallons your tank holds in setup, and when hunting for deals you’d tell it either how full your tank is or, alternately, how much you’re willing to spend on this gas run.
With all that data, it’s not hard to calculate how much the “real” price of the gas run would be. However, it is time consuming and I am an American after all, so I am lazy at heart. So I’d like my phone or GPS unit to quickly calculate the better deal.
For those of you not lazy, but who have never pondered the problem, here is the basic math of the problem.
First, the cost of getting to and from a particular station is:
Where p is the price per gallon at the station in question, d is the distance (in miles) to that station, and m is your average MPG.
So let’s take this morning and my home as an example. I get about 26 MPG in the city. The closest gas station to me is a Major station 1.1 miles away. This morning they’re selling gas for $3.419. So the cost of a gas run to them is 28.93 cents.
The cheapest gas near me is either at BJ’s Wholesale Club or a Citgo station, both of which are 2.6 miles away (in different directions) at $3.329. They are the closest stations selling gas at a price cheaper than the Major station so we will use them as our alternative. The cost of a gas run to them is 66.58 cents.
The difference between those two numbers is 37.65 cents. That’s how much more it will cost me to drive to BJ’s or the Citgo than up the block to the Major.
Now let’s calculate the difference in price between the two stations.
The cheaper station (as compared to the closest) is 9 cents a gallon less.
I have a 15 gallon tank, and let’s say that I’m hovering around a quarter tank right now and need to fill up. I’ll need about 11 gallons to do so, so the cheaper station will cost me 99 cents less. I will save more than I will spend driving the extra distance, so it is worth it.
Now let’s say I need to get gas but am not planning a long drive so there’s no need to fill up. I plan on putting $20.00 in my tank. The cheaper station will give me an additional .158 gallons for the effort. But how much gas did I use to get to each station?
Look familiar? Twice the distance to the station (round trip) divided by your MPG is how much gas you would use to get there.
The closest station (2.2 miles round trip) costs me 0.08 gallons of gas. The cheapest station (5.2 miles round trip) costs me .2 gallons. The farther drive is just barely worth it. If I’d only planned on putting $10.00 in my tank, it would be a waste (using an extra .12 gallons to get an additional .08 gallons).
As I said the math is easy, but takes about a minute with a pencil or calculator. It would be nice if Gasbuddy (or a similar app) could do the calculations in a few flops and tell me automatically which station I should go to.