A CNG car usually costs more to buy than the same car with a petrol engine. You get that money back a little at a time, every kilometre, because CNG costs less per kilometre. The question is how long that takes, and whether it happens before you sell the car.
Start with the cost per kilometre
Divide the fuel price by the mileage. With Lucknow prices (petrol ₹101.86 a litre on 19 October 2026; CNG ₹107.00 a kg from 3 October 2026, Green Gas Limited) and an illustrative car doing 18 km a litre on petrol and 26 km a kg on CNG:
- Petrol: ₹101.86 ÷ 18 = ₹5.66 a km
- CNG: ₹107.00 ÷ 26 = ₹4.12 a km
| Petrol | CNG | |
|---|---|---|
| Fuel price | ₹101.86 a litre | ₹107.00 a kg |
| Mileage | 18 km a litre | 26 km a kg |
| Cost a km | ₹5.66 | ₹4.12 |
| Fuel for 1,800 km a month | ₹10,186 | ₹7,408 |
Lucknow prices: petrol on 19 October 2026, CNG from 3 October 2026 (Green Gas Limited). Mileages are illustrative.
That is ₹1.54 saved on every kilometre. At 1,800 km a month, about ₹2,778 a month.
Then divide the extra price by the monthly saving
If the CNG car costs ₹90,000 more, the simple answer is ₹90,000 ÷ ₹2,778 = about 32 months.
But that ₹90,000 is not free. Either you borrow it or you could have invested it. At 9% a year, the extra price grows while you wait for the savings to catch up, and break-even moves to 46 months. That is the number our tool shows as the headline, because it is the honest one.
Distance decides most of it
The saving is per kilometre, so the less you drive, the longer the wait. With these figures, below about 1,191 km a month the CNG car never earns back its extra price within 10 years, and petrol is the cheaper car overall.
- 1,000 km a month
- 1,800 km a month
- 2,500 km a month
Years from buying
See the numbers
| Years from buying | 1,000 km a month | 1,800 km a month | 2,500 km a month |
|---|---|---|---|
| Today | −₹90,000 | −₹90,000 | −₹90,000 |
| Year 1 | −₹79,921 | −₹65,103 | −₹52,137 |
| Year 2 | −₹70,633 | −₹40,998 | −₹15,067 |
| Year 3 | −₹62,212 | −₹17,759 | ₹21,137 |
| Year 4 | −₹54,738 | ₹4,532 | ₹56,394 |
| Year 5 | −₹48,301 | ₹25,787 | ₹90,614 |
| Year 6 | −₹42,997 | ₹45,908 | ₹1.24 lakh |
| Year 7 | −₹38,934 | ₹64,790 | ₹1.56 lakh |
| Year 8 | −₹36,227 | ₹82,315 | ₹1.86 lakh |
| Year 9 | −₹35,003 | ₹98,356 | ₹2.15 lakh |
| Year 10 | −₹35,402 | ₹1.13 lakh | ₹2.42 lakh |
Savings so far, less the ₹90,000 extra price with 9% a year interest. Above zero, the CNG car has paid for itself.
| Driven a month | Saves a month | Pays back | After 10 years |
|---|---|---|---|
| 800 km | ₹1,235 | Not in 10 years | Petrol ahead ₹72,446 |
| 1,000 km | ₹1,544 | Not in 10 years | Petrol ahead ₹35,402 |
| 1,500 km | ₹2,315 | 62 months | CNG ahead ₹57,209 |
| 1,800 km | ₹2,778 | 46 months | CNG ahead ₹1.13 lakh |
| 2,500 km | ₹3,859 | 29 months | CNG ahead ₹2.42 lakh |
Pays back: the month the savings cover the extra price with interest.
If you drive a lot, the opposite happens. Over 10 years at 1,800 km a month, the CNG car ends up about ₹1.13 lakh ahead after paying for its extra price and the interest on it.
Try it
Your distance and your pump prices
- Saved a month
- ₹2,778
- Pays back, counting interest
- 46 months
- CNG ahead after 10 years
- ₹1.13 lakh
Petrol costs ₹5.66 a km, CNG ₹4.12.
Starts at Lucknow prices. 18 km a litre and 26 km a kg, 9% a year interest on the extra price, prices held flat.
What can change the answer
- Fuel prices. A rise in the CNG price narrows the gap. The tool’s “what would flip the answer” section tells you the CNG price at which petrol starts to win.
- Real mileage. Use what owners of that model report in city traffic, not the brochure figure.
- Running extras. Cylinder testing, kit servicing or a cylinder replacement add costs that petrol does not have. The tool has fields for yearly upkeep and a one-off cost in a given year.
- Resale. If the CNG car sells for less (or more) after a few years, that changes the end result. You can enter each car’s resale value as a share of its price.
Compare all three at once
If you are also considering an EV, choose “All three” in the tool. It shows the total cost of owning each car over the years you choose: price, interest on the price, fuel or charging, upkeep, insurance and resale.
The numbers above are an illustration with today’s Lucknow prices. Put in your own car prices, mileage and distance to get your answer.
For education only. Not investment, tax or insurance advice. Examples use the figures stated in the guide; check your own before you act.