An assumed mileage versus a measured one
Budgeting a 600 km trip with an assumed 15 km/l gives a fuel need of 40 liters, costing ₹4,000 at ₹100/liter — for a total trip cost of ₹8,500 including ₹500 tolls and ₹4,000 food/lodging over 2 days. But a real fill-up on a previous 600 km trip measured only 12 km/l (600 km on 50 liters, per the vehicle's actual fuel efficiency calculation).
Re-running the same trip with the measured figure
Using that real 12 km/l instead of the assumed 15 km/l for the same 600 km trip: fuel needed rises to 50 liters, fuel cost rises to ₹5,000, and the total trip cost rises to ₹9,500 — a full ₹1,000 more than the estimate based on the assumed, more optimistic mileage figure.
Why this gap matters for budgeting
A ₹1,000 difference on an ₹8,500-₹9,500 trip is more than 10% of the total budget, purely from which mileage figure gets typed in. Using a vehicle's own actual, measured mileage — rather than a manufacturer's claimed figure or a rough guess — produces a materially more accurate trip budget.
Parking, a real cost neither calculator includes
Neither the mileage nor the road trip cost calculation accounts for parking. A day with 5 hours of parking at ₹40/hour comes to ₹200; a longer day of 10 hours at the same rate hits a ₹300 daily cap instead of the uncapped ₹400 it would otherwise cost. Adding a realistic parking estimate on top of the fuel/tolls/food total — rather than leaving it out entirely — closes another gap between an estimated budget and the trip's true final cost.