What really decides your car's fuel efficiency beyond the sticker number

That mileage figure in the brochure looks reassuring. A neat number, tested under controlled conditions, promising you'll spend less at the pump.But anyone who's driven a car for more than a week knows the reality rarely matches. The gap between claimed and actual fuel efficiency can be surprisingly wide, and understanding why it exists is the first step to closing it.How manufacturer mileage numbers are actually producedSo how do carmakers arrive at those figures?In India, the Automotive Research Association of India (ARAI) runs standardised tests under strict laboratory conditions. Air conditioning stays off. No potholes, no traffic signals, no impatient auto-rickshaws cutting across lanes.The test cycle mixes acceleration, cruising, and deceleration at predetermined speeds, built to produce a repeatable benchmark rather than simulate your Monday morning commute.That's not a flaw. It's the point. Standardised testing lets buyers compare cars on a level playing field.The problem starts when people treat these numbers as a personal promise rather than a reference point. Real-world figures typically fall meaningfully short of the test number.Buyers researching a used Alto K10 mileage often notice this exact pattern: owner-reported figures cluster well below the official claim, but the car still turns out to be efficient by real-world standards.The benchmark was never meant to be a guarantee. It's a yardstick.The hidden variables that eat into your mileageStart with driving behaviour, because it hits harder than most people expect.Aggressive acceleration from every traffic light, late braking, cruising well above highway speeds - all of it pushes consumption up fast. Smooth, anticipatory driving - easing off the throttle early, coasting toward a red light - can improve efficiency by a noticeable margin without making the journey any slower.The part nobody tells you is how quickly those habits compound. A week of smoother inputs and you'll see it in the numbers.Then there's weight. Every extra kilogram requires energy to move. A boot full of forgotten gym bags, old water bottles, and a child seat nobody's used in months is dead weight you're paying to haul around every single day.Roof racks are sneaky too. Even empty ones create aerodynamic drag that worsens at highway speeds, quietly bleeding efficiency in a way the fuel gauge takes a while to expose.Tyre pressure is another quiet culprit. Under-inflated tyres increase rolling resistance, forcing the engine to work harder for the same output. Checking pressures fortnightly costs nothing. Most people skip it. Don't.Climate control deserves a mention. Running the AC in stop-and-go city traffic places a continuous load on the engine. That load is real, it's constant, and in a small-displacement car it shows up fast.In cooler weather, opening windows at low speeds makes a genuine difference. At moderate highway speeds, though, open windows create more drag than the AC compressor draws, so the crossover point matters more than most drivers realise.Why older cars behave differently than new onesThis is what worries most buyers looking at pre-owned vehicles. Does mileage drop as a car ages?The honest answer: it depends on maintenance history far more than on age itself.Most people assume older automatically means worse fuel economy. That's only half the story. A well-maintained engine with clean injectors, fresh spark plugs, and a properly functioning oxygen sensor will perform close to its original efficiency even after several years.Well-kept cars routinely return figures that rival newer models, because someone actually followed the service schedule.Neglected servicing lets small inefficiencies compound quietly. Clogged air filters restrict airflow. Degraded engine oil increases internal friction. A faulty thermostat can keep the engine running rich, burning fuel it doesn't need to burn on every single trip.Buyers working through a 2nd hand Celerio mileage guide will find that well-kept examples still deliver strong figures.The lightweight construction and efficient engine in cars like the Celerio mean age-related losses stay modest, provided the basics have been looked after. Service records before purchasing aren't optional. They're your single best predictor of the fuel economy you'll actually live with.Practical steps to get closer to the claimed figureHere's what consistently works:●     Service on schedule. Oil changes, air filter replacements, spark plug swaps at recommended intervals keep the engine breathing properly.●     Monitor tyre health. Correct pressures, balanced wheels, aligned suspension all cut rolling resistance in different ways and compound over distance.●     Drive smoothly. Gentle acceleration, early throttle lift-off. Matters more than the car's rated output.●     Clear the boot. Items you don't need for the trip don't belong in the car.●     Plan routes. Avoiding congested roads keeps the car in a steady cruise rather than grinding through stop-start cycles that kill efficiency.Disclaimer: This article is published in association with Cars24 and not created by TNM Editorial.