The EV question sounds simple: "Will I save money?" The honest answer is that it depends on four numbers most people have never actually measured. Here is how to do the arithmetic before you walk into a showroom.
Every few months the EV-vs-petrol debate flares up on every group chat and office lunch table. Someone posts a screenshot showing "₹1.2 per km on electricity vs ₹8 on petrol" and the replies split between the convinced and the sceptical. Both camps are usually working from the wrong numbers, because the right numbers are the ones specific to your vehicle, your city, and your actual driving pattern, not a national average, not a YouTube reviewer's commute in Bengaluru.
The math is not complicated. It requires four inputs, and most petrol-car owners do not have even one of them measured accurately. Let's get them on paper before the EV decision gets anywhere near a test drive.
The Four Numbers That Actually Decide the Answer
Running cost per kilometre for any vehicle, petrol or electric, comes down to the same structure: fuel (or energy) cost divided by efficiency. The complication is that both the numerator and denominator shift by city, by season, and by driving habit. A flat ₹/km figure printed in a brochure is a best-case number under controlled conditions. Your number will be different.
For a petrol car you need: current petrol price in your city and your real tank-to-tank mileage. For an EV you need: your effective per-unit electricity cost and the real-world km/kWh your EV will deliver on your routes. That last one you can only estimate before purchase, but you can bracket it reasonably.
Step 1: Know What Your Petrol Car Actually Costs Per Kilometre Right Now
Most drivers quote the ARAI figure when someone asks about mileage. That number is a laboratory result measured on a fixed drive cycle. It does not include your 45-minute crawl through Andheri at 8:30 AM, the AC running full blast in May, the three traffic signals per kilometre in Lajpat Nagar, or the fact that you have been driving on tyres inflated to 28 PSI instead of 34.
The only mileage that matters for this calculation is your actual tank-to-tank average across at least three to four fill-ups. That is: litres pumped divided into kilometres driven since the last full fill. If you have been logging fill-ups consistently, pull the last six to eight entries and average them. That average is your real efficiency number.
Then the petrol cost per km calculation is straightforward:
₹/km = petrol price per litre ÷ km per litre
Example (Delhi, Aug 2026):
Petrol: ₹94.77/litre
Real mileage (city): 11.2 km/l
Cost per km: ₹94.77 ÷ 11.2 = ₹8.46/km
Now add the non-fuel costs: servicing, oil changes, consumables. For a mass-market petrol hatchback, scheduled service typically runs ₹4,000 to ₹8,000 every 10,000 km depending on brand and city labour rates. That adds roughly ₹0.40 to ₹0.80 per km on top of fuel. If you are honest about this, your petrol car's operating cost is probably ₹9 to ₹11 per km in city conditions.
If you have not been logging fill-ups, you are guessing, and guessing in the direction that makes your current situation look better than it is. The tank-to-tank method is the only way to get a real number, and it takes about 30 seconds at each fill-up to capture.
One thing to account for on petrol: since April 2026, all petrol at Indian pumps is E20. If your vehicle is more than a few years old, your real mileage may already be slightly lower than it was on earlier blends. If you have been tracking fill-ups through this transition, your log will show this clearly. If you haven't, check out the two-tank experiment method to isolate the E20 effect before you use your current mileage as a baseline for the EV comparison.
Step 2: Build the EV Cost Per Kilometre Before You Own One
The electricity cost side is where most EV cost comparisons go wrong, in two different directions.
Optimists use the home-charging rate divided by the claimed range, which gives numbers around ₹1 to ₹1.5 per km. Pessimists use public fast-charger rates, which in 2026 typically run ₹18 to ₹25 per kWh at third-party stations, giving numbers much closer to petrol. The honest answer is somewhere in between, weighted by how you will actually charge.
Start with your electricity rate. If you live in a flat and cannot install a home charger, your charging will be mostly public, and the ₹/km math changes dramatically. If you have a ground-floor parking spot with access to a 15-amp socket, home charging at your domestic tariff (typically ₹6 to ₹9 per kWh depending on slab and city) is realistic most of the time.
Then bracket the real-world efficiency. Manufacturer-claimed range figures are measured at moderate speeds, mild temperatures, no AC. In city traffic with AC in Indian summer, expect 15 to 25% less range than claimed. On the highway at 100+ km/h, expect 20 to 30% less. So if a vehicle claims 400 km of range from a 40 kWh battery (implying 10 km/kWh), plan for 7 to 8 km/kWh in real mixed use.
EV ₹/km at home charging:
Electricity rate: ₹7.50/kWh (mid-slab, Mumbai domestic)
Real efficiency: 7.5 km/kWh
Cost per km: ₹7.50 ÷ 7.5 = ₹1.00/km
EV ₹/km at public fast-charger:
Rate: ₹22/kWh
Real efficiency: 7.5 km/kWh
Cost per km: ₹22 ÷ 7.5 = ₹2.93/km
Blended (70% home, 30% public):
(0.70 × ₹1.00) + (0.30 × ₹2.93) = ₹0.70 + ₹0.88 = ₹1.58/km
Add EV servicing. It is genuinely lower: no oil, no timing belt, fewer brake replacements due to regenerative braking. But tyres wear at roughly the same rate (sometimes faster due to immediate torque), and battery health monitoring becomes a relevant cost factor after year 5. Budget ₹0.20 to ₹0.40 per km for EV servicing and consumables on a new vehicle.
So in this worked example: petrol car at ₹9 to ₹11 per km versus EV at ₹1.80 to ₹2.20 per km (blended charging plus servicing). The gap is real. But it does not decide the question by itself, because of the purchase price differential.
Step 3: The Break-Even on the Purchase Premium
A comparable EV typically costs ₹3 to ₹10 lakh more at purchase than its petrol equivalent, depending on segment. That premium has to be recovered through lower running costs before you come out ahead.
Break-even distance calculation:
Purchase premium: ₹5,00,000
Petrol ₹/km (all-in): ₹10.00
EV ₹/km (all-in): ₹2.00
Saving per km: ₹8.00
Break-even: ₹5,00,000 ÷ ₹8.00 = 62,500 km
At 15,000 km per year of city driving, that is just over four years. At 8,000 km per year (a typical second-car situation), it is nearly eight years. These are not arguments against EVs, they are arguments for doing the arithmetic with your own numbers before assuming the decision is obvious.
If you are not logging your current fuel costs and real mileage, you cannot calculate the saving per km with any accuracy. You are comparing a vague feeling about petrol spend against a brochure number for EV efficiency.
Bharometer
Log every fill-up, get your real ₹/km, and have the actual numbers ready before any EV showroom conversation.
What Changes If You Drive Mostly Highway
The petrol-vs-EV math shifts noticeably on intercity routes. Petrol cars get better mileage at steady highway speeds; a car that does 11 km/l in the city often returns 15 to 17 km/l on NH48 at 90 km/h. Your ₹/km for long trips drops to ₹5.50 to ₹6.50. Meanwhile, EV efficiency on the highway drops relative to city driving, and charging infrastructure along most Indian national highways is still thin enough that you may be using fast-charger rates for top-ups. The gap narrows substantially for a heavy highway driver.
This is also why one number cannot represent your situation. If you drive Delhi-Agra twice a month and city the rest of the time, your real petrol cost profile is a weighted mix of both. The same will be true for your EV. If you track fill-ups by trip type, which a fuel log lets you do, you can build the weighted average rather than guessing.
The highway vs city mileage piece covers why a single km/l figure hides this variation, and the same logic applies here: knowing your split is the only way to build an honest cost comparison.
The Variables You Cannot Control But Should Know
Petrol prices in India are revised by oil marketing companies and passed to the pump. They have moved significantly in both directions over five-year windows. If petrol climbs from ₹95 to ₹115 per litre over the next three years, your break-even point shortens considerably. If it stays flat, it doesn't. You cannot forecast this, but you can note that the EV running cost has a much smaller exposure to crude oil price movements, your electricity tariff can rise, but it tends to be slower and more gradual.
Battery degradation is the corresponding EV-specific variable. Most EVs sold today carry 8-year, 1.6-lakh-km battery warranties in India. After that window, a degraded battery with 80% of original capacity means your real-world range and ₹/km efficiency will drift. This is a legitimate long-term cost factor that a five-year break-even calculation ignores.
Neither of these should paralyse the decision. They should just be named rather than swept under the marketing language on both sides.
Running the Numbers: A 10-Minute Exercise
Here is the practical sequence before any EV purchase conversation:
- Pull your last six fill-up logs. Calculate your real km/l average. If you haven't been logging, start now and wait three tanks before comparing anything. The real average method takes one fill-up to set up and three to get a reliable number.
- Divide your city's current petrol price by that km/l figure. Add ₹0.50 to ₹0.80 per km for servicing. Write that number down: it's your current all-in petrol ₹/km.
- For the EV you're considering, get the battery size in kWh and the claimed range. Knock 20% off the claimed range for a realistic city figure. Your expected efficiency is battery kWh divided by that reduced range number.
- Estimate your charging split: what percentage will realistically be home charging at your domestic tariff vs public chargers? Calculate the blended electricity ₹/kWh, then divide by your expected efficiency to get EV ₹/km.
- Subtract EV ₹/km from petrol ₹/km to get your saving per km. Divide the purchase price premium by that saving. That's your break-even in kilometres.
- Compare the break-even to your annual mileage. If you do 12,000 km a year, a 60,000 km break-even is five years. If you do 20,000 km, it's three.
That is the actual decision framework, and the only input you control fully is step 1. Every other number is publicly available or estimable from specs. The one number that is uniquely yours, and the one that most people cannot produce without a log, is their real mileage right now.
Bharometer tracks petrol, diesel, and CNG fill-ups with a pump-scan feature that photographs the pump screen and fills in litres, amount, and rate automatically. It calculates your running ₹/km so you always have a current, accurate baseline. When the EV conversation comes up, you are not guessing what your petrol car costs you: you have a number, and it is the right number.
The EV switch can make financial sense for a lot of Indian drivers, particularly urban ones with home charging access and annual mileage above 12,000 km. Whether it makes sense for you specifically depends on inputs that only your own log can supply. Start there, before the showroom.