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How much does E20 reduce mileage?
The mileage drop from E20 is small — roughly 1% to 6% depending on the vehicle, not the 7–10% often claimed in viral posts.
Estimates put it at about 1–2% for E10 vehicles calibrated for E20, and around 3–6% for those not tuned for it. Industry body SIAM has cited figures in the 2–4% range.
Why it happens
Ethanol contains less energy per litre than petrol, so your engine uses a little more fuel for the same work. It is physics, not a fault.
Worth worrying about?
For most drivers it is a few rupees per tank, and newer E20-tuned engines narrow the gap. The calculator on the homepage estimates the rupee impact from your mileage and monthly running.
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Is the mileage loss permanent?
It is not damage — it is the normal effect of ethanol's lower energy density, and varies by vehicle.
Do E20-tuned cars lose less?
Yes. Engines calibrated or designed for E20 minimise the difference.