At a glance
- Cheapest to run
- Electric, then CNG
- Cheapest to buy
- Petrol
- Key number
- How many km you drive a year
- GST on EVs
- 5% (petrol small cars: 18%)
- Formula
- Fuel price ÷ km per unit
Example figures below are illustrations. Use your own city’s prices.
Petrol is cheaper to buy, CNG is cheaper to run, and electric is cheapest to run of all but usually costs the most up front. Which one saves you money depends almost entirely on how far you drive and for how many years you keep the car.
This guide gives you a simple method to work it out for your own case, a worked example, and the practical points that numbers alone do not show.
Key takeaways
- Work out cost per km: fuel price divided by kilometres per litre, kg or kWh.
- The extra price of CNG or electric pays back faster the more you drive.
- Home charging is what makes an EV cheap to run. Public fast charging costs more.
- CNG means a smaller boot and a fuel network that is uneven outside big cities.
Step 1: cost per kilometre
Divide the price of one unit of fuel by how far the car goes on that unit. Use real-world figures, not only the claimed ARAI or MIDC numbers, which are measured in test conditions.
| Fuel | Example price | Example efficiency | Cost per km |
|---|---|---|---|
| Petrol | ₹100 per litre | 15 km per litre | ₹6.7 |
| CNG | ₹80 per kg | 22 km per kg | ₹3.6 |
| Electric (home charging) | ₹8 per unit | 7 km per kWh | ₹1.1 |
These are round figures to show the method. Fuel and electricity prices change by city and month, and your car’s efficiency depends on traffic, load and driving style.
Step 2: the break-even point
Take the extra price you pay for the CNG or electric version, and divide it by how much you save per km. The answer is how many kilometres it takes to recover the extra cost.
Using the example above, a CNG car saves about ₹3 per km over petrol. If the CNG version costs ₹90,000 more, you break even after about 30,000 km. An electric car saves about ₹5.5 per km; if it costs ₹4 lakh more, break-even comes after about 72,000 km.
| Yearly driving | CNG break-even | EV break-even |
|---|---|---|
| 8,000 km | About 3.7 years | About 9 years |
| 15,000 km | About 2 years | About 4.8 years |
| 25,000 km | About 1.2 years | About 2.9 years |
Lower GST and road-tax waivers on EVs in many states can cut the price gap, which brings the EV break-even closer. Check your state’s rules.
What the numbers do not show
Electric
- Lowest running cost with home charging
- Fewer moving parts, simpler servicing
- Quiet and smooth in traffic
Electric
- Highest purchase price
- Long trips need planning around fast chargers
- Needs a parking spot where you can charge
CNG makes the most sense for high daily running in cities with good CNG stations. The cylinder takes boot space in many models, though some newer cars use twin smaller cylinders to free up room. Petrol remains the simplest choice if you drive under about 8,000 km a year: the savings from other fuels take too long to recover the higher price.
Track your driving for one normal month before you decide. Most people guess their yearly kilometres wrong, and that one number decides the answer.
Servicing, warranty and resale
Running cost is not only fuel. Electric cars have no engine oil, spark plugs or clutch, so routine service bills are usually smaller, but the battery is the most expensive part of the car. Check the battery warranty in years and kilometres before you buy, and read what counts as a warranty claim.
CNG kits need periodic checks, and the cylinder must be tested and certified at fixed intervals under the rules for gas cylinders. A factory-fitted CNG car keeps the maker’s warranty, which is a strong reason to avoid aftermarket kits.
Resale is harder to predict. Petrol cars have the most established used market. Demand for used EVs is growing but buyers will ask about battery health, so keep your service and charging records.
Which one to choose
Drive little and mostly in town: petrol. Drive a lot in a city with good CNG supply: CNG. Can charge at home and keep cars for five years or more: electric.
Questions buyers ask
Is CNG cheaper than an electric car?
Per kilometre, electric with home charging is usually cheaper. But CNG cars cost less to buy, so CNG can work out cheaper overall if you do not drive enough to recover the EV’s higher price.
Does fast charging change the maths?
Yes. Public DC fast charging costs much more per unit than home electricity, which raises the cost per km.
Is the claimed mileage what I will get?
Usually not. ARAI and MIDC figures come from standard test cycles. Real-world numbers are often lower.
