Monthly fuel cost = Fuel required × Price per litre
Yearly fuel cost = Monthly fuel cost × 12
A handy shortcut falls out of this: fuel cost per km = price per litre ÷ mileage. Multiply that by any distance to estimate its fuel cost.
Worked Example
Suppose you drive 1,200 km a month in a car that gives 15 km per litre, and petrol costs ₹103 per litre. You need 1,200 ÷ 15 = 80 litres a month, which costs 80 × 103 = ₹8,240. Over a year that is ₹98,880, or about ₹6.87 per km.
Small changes add up. In the same example, a ₹5 rise in the price per litre adds ₹400 a month (₹4,800 a year). If your real mileage is 14 km per litre instead of 15, you spend about ₹589 more each month, roughly ₹7,060 a year.
How Mileage Changes Your Fuel Bill
For 1,200 km a month at an illustrative ₹100 per litre:
Mileage (km/l)
Cost per km
Monthly cost
Yearly cost
10
₹10.00
₹12,000
₹1,44,000
15
₹6.67
₹8,000
₹96,000
20
₹5.00
₹6,000
₹72,000
25
₹4.00
₹4,800
₹57,600
45
₹2.22
₹2,667
₹32,000
The lower rows are typical of small cars and the last of commuter motorcycles. Moving from 10 to 15 km per litre saves far more than moving from 20 to 25, because cost per km falls less with each extra km per litre.
Getting a Realistic Estimate
Use your real mileage, not the brochure figure. The certified figure comes from a standard lab test and is usually higher than what you get in city traffic with the AC on. A full-tank-to-full-tank check with the Mileage Calculator gives a truer number.
Estimate monthly distance from your odometer over a few weeks rather than guessing. A 25 km each-way commute over 22 working days is already 1,100 km before weekend trips.
Fuel prices differ from state to state because of VAT and are revised from time to time, so use the price at the pump you actually fill from. Oil marketing companies publish daily prices by city on their websites and apps.
For CNG, enter mileage in km per kg and the price per kg. The arithmetic is identical; the result is in kg instead of litres even though the label says litres.
Frequently Asked Questions
Check your vehicle's manual for the manufacturer-claimed mileage, or better, use the Mileage Calculator to work out your vehicle's real-world mileage from your own distance and fuel consumption.
No, this is designed for your regular, recurring monthly driving - like a daily commute. For a one-off trip, use the Trip Fuel Cost Calculator instead, which supports a round-trip option.
No, this calculates fuel cost only. Use the Vehicle Running Cost Calculator for a complete monthly cost of ownership, including maintenance and insurance.
Divide the fuel price by your mileage. At ₹103 per litre and 15 km per litre, fuel costs about ₹6.87 per km. You can also divide the Monthly Fuel Cost shown here by your monthly distance.
The usual reasons are a lower real-world mileage than the figure you entered, more kilometres driven than planned, or a price change during the month. Traffic, idling, AC use, under-inflated tyres and short trips with a cold engine all reduce mileage.