How Much Will Gas Cost for My Road Trip?

Two numbers worth having before you leave

A 500-mile trip each way, in a car doing 28 mpg, at $3.40 a gallon:

$121.43 of fuel. Split two ways, $60.71 each.

The second number is the one to agree on at the kitchen table. Working it out at a service station three hundred miles in — when one person has paid for two fill-ups and someone else bought the snacks — is where road trips go quietly wrong.

The arithmetic

500 miles each way, returning:

500 × 2 = 1,000 miles

1,000 ÷ 28 mpg = 35.7 gallons

35.7 × $3.40 = $121.43

÷ 2 people = $60.71 each

Enter the distance one way and leave coming back again ticked — the calculator doubles it. Untick it for a genuine one-way run: moving house, delivering a car, or flying home and leaving it behind. That single tick is the most common way this sort of estimate comes out half the real figure.

The other number: what a mile costs

$3.40 ÷ 28 mpg = $0.12 per mile.

This is the figure that makes route decisions easy. A fifty-mile detour to see something is about six dollars of fuel — which is usually far less than people assume, and often settles the question on the spot.

It's also the honest answer when someone asks what a lift is worth.

Your MPG is the number this stands or falls on

Everything else you enter is a fact. The MPG is an estimate, and the window-sticker figure is usually optimistic for a real trip.

Rated figures come from steady, moderate-speed cruising. A real road trip has:

• Sustained high speeds — air resistance climbs sharply, and the fuel to push through it climbs faster than the speed does
• A loaded car, and often a roof box, which costs MPG for the entire journey whether it's full or not
• Hills, headwinds, air conditioning, winter fuel

If your dashboard shows a long-run average, use that. It already includes how you actually drive, which no published rating can.

And write your odometer down before you go. Miles travelled ÷ gallons put in is your real MPG — worth knowing for the return leg and every trip after.

Fuel is not the trip cost

Worth being blunt about, because this calculator deliberately does one thing.

Not included: tolls, parking, food, accommodation, and vehicle wear.

The last one is the one people forget, because it doesn't arrive at the pump. It shows up months later as tyres, brakes and a service that came round sooner than expected. Per-mile running costs for a car are typically several times the fuel alone.

So treat $121.43 as the pump total, not the trip total.

Two cars or one?

One full car, essentially always.

Two cars means running the numbers twice — each with its own MPG — and splitting within each. It roughly doubles the fuel to move the same people. That's the real argument for squeezing in, and it's usually worth more than the comfort you're trading.

Swapping drivers, by contrast, changes nothing. The fuel depends on the distance and the car, not who's holding the wheel.

Splitting it fairly when it isn't simple

An even split assumes everyone travels the whole way. Often they don't.

The clean way to handle someone joining partway is the cost per mile: multiply it by the miles they're actually in the car, and split the rest between the others. At twelve cents a mile that's a sum anyone can do in their head, and it feels fair because it obviously is.

Two other conventions worth settling out loud before you go, because both cause more friction than the money involved:

• Does the car's owner pay a share? They're already absorbing the wear, which is real and invisible. Many groups have the owner drive and everyone else cover the fuel — but only if it's said in advance.
• Do snacks and coffee go in the pot, or is it fuel only? Either answer works. An unspoken assumption doesn't.

What about an electric car?

Not this calculator. The arithmetic is the same shape but the units are wrong — you'd want miles per kilowatt-hour and a price per kilowatt-hour.

Charging cost also varies far more than petrol does: plugging in at home overnight and stopping at a rapid charger on the road are different prices for the same electricity, so a single figure means less than it does at a pump.

Print the road trip budget sheet — it has the fuel maths at the top and, more usefully, room for all the costs that aren't fuel.