Nikhil Kapoor's diesel SUV has been faultless for eight years. It starts every morning, the service book is complete and nothing about it feels finished. He bought it in Delhi in 2018, which makes it a BS4 car and diesel vehicles in the capital region are registered for ten years rather than fifteen. At 44, with a car he still likes, he is facing a question, does he upgrade now or run it to the end?
BS4 stands for Bharat Stage 4 and BS6 for Bharat Stage 6, the standards that cap what a vehicle may emit from its exhaust. India switched on 1 April 2020, skipping BS5 altogether, so every BS4 car on the road is at least six years old today. Your BS4 car remains entirely legal to own and drive. The upgrade question is not about legality, it is about arithmetic. How many years of registration remain, what the car is worth while it still has them and what the switch is worth to you in tax rebates and insurance discounts you may not know you hold.
What do BS4 and BS6 stand for?
Bharat Stage Emission Standards cap the pollutants a vehicle's engine may release. The Central Pollution Control Board is set under the Ministry of Environment, Forest and Climate Change, modelled on Europe's norms. The series began with India 2000, then BS2 in 2005, BS3 in 2010 and BS4 in 2017. India skipped BS5 to close the gap with international standards in one step rather than two.
Term | Full form | In force from |
|---|---|---|
BS4 / BS-IV | Bharat Stage 4 | 2017 |
BS6 / BS-VI | Bharat Stage 6 | 1 April 2020 |
BS6 Phase 2 | Bharat Stage 6, second phase | 1 April 2023 |
CoD | Certificate of Deposit, issued when a vehicle is scrapped | Ongoing |
NCB | No Claim Bonus, an insurance discount | Ongoing |
What is the difference between a BS4 and a BS6 engine?
BS6 tightened the permitted limits, especially for diesel.
Fuel | Pollutant | BS4 limit | BS6 limit |
|---|---|---|---|
Petrol | Nitrogen oxides (NOx) | 80 mg/km | 60 mg/km |
Petrol | Particulate matter (PM) | Not specified | 4.5 mg/km |
Diesel | Nitrogen oxides (NOx) | 250 mg/km | 80 mg/km |
Diesel | Particulate matter (PM) | 25 mg/km | 4.5 mg/km |
Diesel | Hydrocarbons + NOx | 300 mg/km | 170 mg/km |
Nitrogen oxide limits for diesel fell by roughly 70 per cent and particulate matter by around 80 per cent. Meeting those numbers took new hardware, which is the difference under the bonnet.
Component | BS4 | BS6 |
|---|---|---|
Diesel Particulate Filter (DPF), traps soot | Not required | Fitted to diesels |
Selective Catalytic Reduction (SCR), treats NOx | Not required | Used on many diesels |
Onboard Diagnostics (OBD), monitors emission systems | Limited | Standard |
Real Driving Emissions (RDE), tests on road rather than only in a lab | Not required | Added in BS6 Phase 2 |
Fuel sulphur content | 50 ppm | 10 ppm |
BS6 petrol and diesel also contain 10 parts per million of sulphur, compared with 50 ppm in BS4 fuel. Lower sulphur is what lets the newer filters and converters work, which is why fuel and engine were upgraded together.
Are BS4 cars banned in India?
No, this is worth stating plainly because it is where most of the worry starts.
On 31 March 2020, the sale and registration of new BS4 vehicles ended. Cars already registered remain legal for their full registration period and you can drive, sell and transfer ownership normally. Your BS4 car needs exactly what any car needs: valid registration, valid insurance and a current Pollution Under Control certificate.
How many years can your BS4 car still run?
This is the number that decides everything else and it is the part the older explainers never had to answer.
A private car's registration lasts 15 years, after which it can be renewed in 5-year blocks, subject to a fitness test. Delhi NCR is the exception that matters, where diesel vehicles are capped at 10 years and petrol at 15 years under directions that predate the central rules.
Where your car is registered | Petrol BS4 | Diesel BS4 |
|---|---|---|
Most of India | 15 years, then renewable in 5-year blocks, subject to fitness | 15 years, then renewable in 5-year blocks, subject to fitness |
Delhi NCR | 15 years from registration | 10 years from registration |
Read the diesel row twice if you live near the capital. Nikhil's 2018 diesel reaches its limit in 2028, which is two years away, not eight.
Check your own date rather than estimating it. Your registration certificate carries it and Parivahan lists it against your registration number.
Can a BS4 car run on BS6 fuel?
Yes and it has since 2020, because BS6 fuel is all the pumps sell. It is more refined than the BS4 engines it was designed around, so petrol cars run on it without issue. For BS4 diesels, manufacturers indicated no significant short-term concern, though some engineers noted the lower sulphur content, which also contributes to lubrication, could tell over the long term. Millions of BS4 diesels have now run on BS6 fuel for six years.
Should you upgrade your BS4 car now or run it longer?
Most owners assume running a good car to the end is the thrifty choice. Often it is. The case worth examining is where it quietly is not.
Resale value does not slide gently towards a registration deadline, it steps down as the date approaches because the pool of buyers shrinks. A Delhi diesel with two years left can only be sold to someone who will take it out of NCR and re-register it, a much smaller market than the one that existed three years ago. The value you protect by holding on is the value that disappears while you hold on.
That reasoning does not travel to every car. Run the four checks.
Check | What it tells you |
|---|---|
Years of registration remaining | Under three years, the resale window is closing. Over eight, there is no hurry |
Fuel type and city | Diesel in NCR has a fixed and near horizon. Petrol elsewhere has a long one |
Current condition and running costs | A sound car with years left is usually more cost-effective to keep than to replace |
What the switch pays you | Scrappage benefits and your No Claim Bonus both have value and both are covered below |
If you are deciding between upgrading now and holding on, upgrade while the car still has resale value and years of registration to sell, which usually means acting before the last two or three years rather than during them. Hold on, when the car is sound, the registration runs well past 2030 and nothing about your usage has changed. The trigger is the calendar, not the badge.
What does the scrappage policy give you if you upgrade?
Worth knowing before you trade the car in, since most owners never consider this route. Scrap a vehicle at a Registered Vehicle Scrapping Facility rather than selling it and you receive a Certificate of Deposit, which unlocks benefits when you buy the replacement.
Benefit | What it means |
|---|---|
Road tax rebate | Up to 25 per cent on the new private vehicle, varying by state |
Registration fee waiver | On the new vehicle |
Manufacturer discount | Offered against a Certificate of Deposit, on terms that change periodically |
Scrap value | Paid to you for the old vehicle separately |
The certificate is valid for three years from issue and only a Registered Vehicle Scrapping Facility can issue one, so an informal dismantler qualifies you for none of it.
Scraping is not automatically better. A car with resale value left is usually worth more sold than scrapped, which is exactly why timing matters. Compare the trade-in price against the scrappage benefits before committing and confirm the current road tax rebate with your state transport department and the manufacturer's offer with the dealer, since both change.
What happens to your insurance when you upgrade?
This is the part owners most often leave on the table and it can be worth thousands. Your No Claim Bonus belongs to you, not to the car. It is a discount on the own-damage portion of your premium, earned for every claim-free year and it rises with each one.
Consecutive claim-free years | No Claim Bonus |
|---|---|
1 | 20% |
2 | 25% |
3 | 35% |
4 | 45% |
5 or more | 50% |
Sell the BS4 car and that discount does not go with it. You carry it over to your new BS6 car by asking your existing insurer for an NCB certificate, which is generally valid for 3 years from the date of issue. Nikhil has been claim-free throughout, which means a 50 per cent discount on the own-damage premium of whatever he buys next. That is a real number on a new car, where the Insured Declared Value is at its highest and the own-damage premium is therefore at its largest.
Three points protect it. The bonus attaches to the policyholder, so keep the new policy in the same name. Renew without leaving a gap, since a lapse beyond the permitted window can reset it to zero. And the rate is set uniformly, so switching insurers costs you nothing, provided you declare the bonus and produce the certificate.
Ask your insurer one exact question before you buy the new car: what NCB certificate can you issue me and how long is it valid? Zurich Kotak General Insurance Company (India) Limited offers comprehensive plans and will apply an accumulated NCB on production of the certificate, subject to policy terms.
Conclusion
Nikhil's decision took one line of arithmetic rather than a test drive. Two years of registration left, a diesel in NCR, a car still worth something today and worth considerably less in eighteen months and a 50 per cent No Claim Bonus waiting to move to whatever came next. He upgraded while the old car still had a market, not after it lost one.
Check your registration date first, then match your fuel type to your city. If the runway is long, enjoy the car; a BS4 car is not a compromised car, only an older one. If the runway is short, move while the car still has value to sell and collect the two things owners routinely forget: the scrappage benefits if you go that route and the No Claim Bonus that was always yours rather than the car's.
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Frequently asked questions
Is a BS4 car illegal to drive in India in 2026?
No. Only the sale and registration of new BS4 vehicles ended on 31 March 2020. A car already registered remains legal for its full registration period, with valid registration, insurance, and a current PUC certificate.
Do I lose my No Claim Bonus when I sell my BS4 car?
No, provided you transfer it. The bonus belongs to the policyholder rather than the vehicle, so you request an NCB certificate from your existing insurer and present it when insuring the new car. The certificate is generally valid for three years from the date of issue.
What is BS6 Phase 2 and does it affect my new car?
BS6 arrived in two phases, with Phase 2 in force from 1 April 2023, adding Real Driving Emissions testing and fuller onboard diagnostics. Any new car you buy today already meets it, so you don't need to ask for it.
Is it better to scrap my old car or sell it?
Sell it while it still has resale value and registration years remaining. Scrapping through a Registered Vehicle Scrapping Facility makes more sense once resale value has thinned, since the Certificate of Deposit brings a road tax rebate, a registration fee waiver and a manufacturer discount on the replacement.
