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300 miles at 28 mpg and $3.40 gas: $36.43 — $9.11 each split four ways. And the EV version of the same trip: $14.57.
The road-trip budget question, answered honestly: distance ÷ MPG × price per gallon. This calculator adds the round-trip toggle, the per-person split that settles group-trip math, and the fuel-only cost per mile — the number that looks cheap until you learn the IRS prices the full cost of driving at roughly 70 cents a mile.
Road trippers use it before booking: 300 miles at 28 mpg and $3.40 gas is $36.43 — split 4 ways, $9.11 each, round-trip toggle built in.
Miles ÷ MPG × price — 300 miles at 28 mpg burns 10.7 gallons, and at $3.40 that is $36.43. The accuracy upgrades: use your car's actual highway MPG (the trip computer's lifetime average, typically 10–20% below the EPA sticker), price gas along the route not at home (remote tourist corridors run 30–50¢ high), and add 10% for detours, traffic, and the wrong exit that cost 12 miles. Round-trip toggle doubles correctly. For groups, the per-person split settles the eternal debate — $9.11 each on a 4-person 300-mile trip is the number that ends arguments. EV alternative for the same trip at 3.5 mi/kWh on home electricity: about $14.57.
Drive usually wins on cash for groups under ~600 miles; fly wins on time and often on TRUE cost for solo travelers. The honest driving number is not the $36 in gas — the IRS mileage rate (70¢/mile in 2025) prices depreciation, tires, maintenance, and insurance: a 300-mile round trip really costs ~$210 in vehicle wear plus fuel. A $150 flight beats that solo, loses to it for a family of four ($840 of driving vs $600 of fares). Time prices honestly too: 5 hours of driving vs 1 hour of flying plus 3 hours of airport. The crossover rule of thumb: solo beyond ~500 miles, fly; family of 3+ under 500 miles, drive. The sleeper variable: a rental car at destination can flip the math back.
Speed is the biggest lever: aerodynamic drag scales with velocity squared, so most cars peak near 50–60 mph and lose roughly 10–15% of MPG going 65 → 75 mph — on a 600-mile day, that is $8–12 for arriving 45 minutes sooner. Next: tires at door-sticker PSI (under-inflation by 10 PSI costs ~1–2%), roof boxes off when empty (a cargo carrier at highway speed costs 10–25%), smooth throttle (aggressive driving burns 15–30% more), and windows up above 45 mph (AC below that, aerodynamics above). Idling burns 0.2–0.5 gal/hour — drive-through lines are fuel bonfires. Realistic combined gain: 15–25% over a lead-foot baseline, which on a 1,200-mile vacation is a free tank of gas.