A road trip budget starts with fuel — and ends up being about four other things. Here's the complete math, starting with the part you can compute before you pack.
Line 1: Fuel (the exact part)
Fuel = total miles ÷ real MPG × price per gallon. Use your measured MPG from a recent tank (the mileage calculator), not the window sticker — loaded cars at 75+ mph run 10–15% below EPA highway. A 2,000-mile loop at 28 MPG and $3.45: $246. The road trip calculator handles round trips and per-passenger splits automatically.
Line 2: The fair split
Splitting fuel evenly is the floor of fairness — the driver's car absorbs the wear. The common convention among road-trippers: fuel split per person, plus a vehicle contribution of $0.05–0.10 per mile to the owner. On a 2,000-mile trip with four people, that's $62 fuel each plus $100–200 to the owner's maintenance fund. Cheap, fair, and it keeps friendships out of the odometer.
Lines 3–6: the forgotten budget
- Tolls and parking: route-dependent and brutally easy to forget — the Northeast corridor can add $100+ to a loop. Check your route's toll schedule; most calculators on toll authority sites do it in one page.
- Service-window items: crossing an oil-change interval mid-trip? Budget it. Tires near replacement? A blowout 800 miles from home is a four-figure line item.
- Food reality: road food costs 2–3× grocery food. A cooler with sandwiches and a case of water is the highest-ROI packing decision of the trip.
- The 15% buffer: detours, one extra hotel night, the aquarium you didn't plan. Pros pad every trip budget 10–15% and call the surplus "memories."
A worked example
2,000-mile loop, four people, 28 MPG, $3.45 gas: fuel $246 ($62 each). Vehicle contribution: $150. Tolls: $60. One hotel night each way: $320. Food: $340 (mix of cooler and stops). Buffer 15%: ~$170. Total ≈ $1,286 — about $322 per person for a week on the road. That's the difference between a trip you planned and a trip that planned you.