Planning a road trip budget without knowing your fuel cost is like packing a suitcase blindfolded — you'll get close, but you'll probably be wrong in an annoying way. Gas prices swing by 50 cents between states, your car's real-world fuel economy is never what the sticker says, and round trips double everything.
Here's how to get a number you can actually budget around.
Figure out your real fuel economy. Your car's rated MPG is measured under lab conditions. Real-world driving — highway speed, AC blasting, roof rack loaded — typically drops it 10-20%. If your car is rated 30 MPG highway, plan for 25-27. Check your trip computer's average over your last few tanks if you want something closer to reality.
Get the distance. Google Maps gives you the mileage. For multi-stop trips, add each leg separately — a 400-mile trip with a detour through mountain roads burns more fuel per mile than 400 flat highway miles.
Look up current gas prices along your route. GasBuddy shows prices by region, but for budgeting, just use the average for the states you're crossing. AAA publishes state-level averages daily.
Run the numbers. For this step, a free fuel cost calculator does the math instantly — enter distance, your car's MPG, and the gas price, and it spits out total gallons needed, total cost, and cost per mile. It handles round trips too, so you don't have to double everything manually.
For a 600-mile round trip in a car getting 26 MPG at $3.40/gallon, you're looking at about 23 gallons and $78 in fuel. That's a meaningful line item if you're splitting costs with passengers or comparing driving versus flying.
One tip: if you're comparing two vehicles for the trip — say your sedan versus a friend's SUV — run both through the calculator side by side. The difference in fuel cost over a long trip can easily be $40-60, which might change whose car you take.
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