Methodology
How we calculate AC electricity costs — and why you can trust the numbers
From BEE Data to Your Bill
BEE 2026 ISEER Data
Every AC model's cooling capacity, power input, and ISEER rating is sourced from the Bureau of Energy Efficiency's 2026 star rating gazette. We do not use manufacturer marketing materials for consumption figures.
State DISCOM Tariff Slabs
Electricity rates for all 28 states are pulled from the latest SERC tariff orders (FY 2025-26). We account for domestic slab rates, fixed charges, and fuel surcharge adjustments where applicable.
Ambient Temperature Correction
BEE tests ACs at 35°C outdoor / 27°C DB indoor. Real Indian summers often exceed 40°C. We apply correction factors from ISHRAE climate zone data so estimates reflect actual summer load, not lab conditions.
Usage Pattern Modelling
Daily hours, seasonal variation, and thermostat setting all affect bills. Our calculator models real household usage curves — not just flat 8-hour runs — to produce estimates within ±10% of actual bills.
Cross-Verification with Real Bills
Before any formula goes live, we compare it against 50+ anonymised electricity bills from users across India. If the median variance exceeds 10%, the formula is recalibrated.
Primary Data Sources
Every number on this site traces back to one of these sources.
| Source | What we use | Update freq |
|---|---|---|
| BEE ISEER Gazette 2026 | Cooling capacity, power input, ISEER ratings | Annually |
| SERC Tariff Orders FY25-26 | Per-unit rates, slab structures, surcharges | Quarterly |
| ISHRAE Climate Handbook | Temperature correction factors by zone | Every 3 years |
| Manufacturer Spec Sheets | Noise levels, WiFi features, warranty terms | Per model launch |
| Anonymised User Bills | Variance validation, formula calibration | Monthly |
Common Methodology Questions
How accurate are the estimates?
For users who input their exact city, AC tonnage, star rating, and daily hours, our median variance against real bills is ±8.3%. The biggest source of error is usually unknown thermostat setting and room insulation quality.
How often is the data updated?
BEE ratings are updated annually (2026 data released Oct 2024). DISCOM tariffs are checked every quarter. Calculator formulas are recalibrated whenever new user bill data shows systematic drift.
Do you account for inverter vs non-inverter?
Yes. Inverter ACs use variable-speed compressors that reduce consumption by 30-40% at partial load. Our calculator applies BEE's ISEER-based partial-load factors rather than simple on/off duty cycle assumptions.
What about voltage fluctuation and stabiliser consumption?
Stabilisers add 1-3% to total consumption. Our base estimates exclude stabiliser load to keep the calculator simple. A note is shown for users in high-fluctuation zones.
Why do my actual bills sometimes differ significantly?
Common reasons: (1) slab-rate jumps — crossing into higher tariff slabs mid-month, (2) old AC with degraded coils — efficiency drops 10-15% per year without service, (3) extreme weather — 45°C+ days can increase load by 20%.
Questions about our methodology? The formulas are maintained by Sulaiman Sekh, HVAC Engineer.
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