The pump clicked off at $40.46 on a Thursday evening in Laurinburg, and I wrote it on the back of the receipt before Wes had the cap screwed back on: 14.0 gallons at $2.89. That is a full tank in our 2017 CR-V, and it is the number I start every trip plan with.
Wes laughs at me for writing on receipts. I laugh at him for checking the tire pressure every time we stop for coffee. We each have our system.
When we started our one-cheap-trip-a-month rule in January, I thought gas would be the scary line. It isn't. Gas turns out to be the most predictable thing we spend money on, as long as you do a little arithmetic before you leave the driveway.
The arithmetic I do at the kitchen table
Our CR-V has about 112,000 miles on it and still gets about 31 miles per gallon on the highway. Around town, with stoplights and the drive-through, it drops to 27 or 28. So I use two numbers depending on the trip.
The formula is nothing fancy, and it fits on the back of the envelope:
- Round-trip miles, from the road atlas, plus about 10 percent for wandering around once we get there.
- Divide by 31 for a highway trip, or by 28 if a lot of it is town driving.
- Multiply by the gas price, rounded up a dime.
Our first trip of the year, Wilmington and Kure Beach at the end of February, came out like this. It is about 105 miles from our place near Maxton down to Kure Beach, so 210 miles there and back. Add the wandering (Fort Fisher, back up to Darren's, out for supper) and I called it 235 miles. Divided by 31, that's 7.6 gallons. Gas was $2.85 that week, so I planned on $2.95. That gave me $22.42, and I put $23 in the trip envelope for gas.
What we really spent: one fill-up on the way home, $21.88. My guess was 54 cents high, which is exactly where I want to be.
Why I round the price up a dime
Prices move. Between the day I plan and the day we drive, gas around here can go up 5 or 10 cents, and the station at the beach exit is almost always more than the one near home. If I plan at the price I saw on Tuesday, I'm short by Sunday. If I plan a dime high, I either break even or I've got a couple of dollars left over for a cup of coffee.
A dime sounds like nothing. On a 235-mile trip it's about 76 cents. On a long weekend to the mountains, say 600 miles, it's closer to two dollars. It isn't about the money so much as never having to dip into the food line to cover gas. I hate moving money between lines. It makes the receipts look like a crossword puzzle.
What a mile actually costs us
Here's the number that surprised me. At $2.95 a gallon and 31 miles to the gallon, our gas costs about 9.5 cents a mile on the highway. In town at 28 miles per gallon it's about 10.5 cents. So a 100-mile round trip is roughly ten dollars in gas, and I can do that in my head now while Wes is backing out of the carport.
That one number changed how I think about where we go. A 40-minute detour to see a lighthouse or a state park is maybe $5 in gas. A motel that's $20 cheaper but 25 miles further out is still a good deal on gas alone, though not always on time. When people ask why we don't just stay home, I tell them a tank of gas will carry the two of us about 430 miles, which is most of the way to anywhere we'd want to go for a weekend.
For our April beach weekend I did the same thing before we left. About 90 miles each way to the south end of Myrtle Beach, call it 200 miles with driving up and down the Grand Strand. Divided by 31 is 6.5 gallons, times $3.05 (I saw $2.95 and rounded up), comes to $19.83. I wrote $20 on the envelope.
Gas isn't the only cost of driving, of course. Tires, oil and the general wear on a car with this many miles are real, and Wes keeps his own list of those. But for planning a weekend, gas is the line that changes with the destination, so it's the one I figure first.
Wes's only comment when I showed him the formula: "You know the car doesn't care what you wrote on the envelope." True. But the envelope cares, and so do I.
If you want to try this, find your own car's real highway mileage first. Fill the tank, reset the trip meter, drive a highway trip, and fill up again. The sticker number and the real number aren't always the same, and ours was about two miles per gallon lower than the window sticker said when the car was new.
