Bill Calculations, Gas Costs and Checklists
Electricity bill calculation in India - worked examples for Delhi and Tamil Nadu (2026)
Step-by-step bill calculations using the Delhi DERC schedule and TNERC Order No. 6 of 2025, with surcharge, subsidy and common mistakes shown in rupees.
To calculate an Indian household electricity bill, work in this order: (1) units from the meter readings, (2) energy charge slab by slab from your SERC's tariff order, (3) fixed charge from your sanctioned load, (4) fuel surcharge (FPPAS/PPAC/FAC) at the rate for that month, (5) electricity duty and other surcharges, then (6) subtract any state subsidy. The examples below follow those steps with two real schedules: the Delhi DERC domestic schedule and the Tamil Nadu TNERC domestic slabs in Suo-motu Order No. 6 of 2025. Surcharge and duty rates in the examples are labelled illustrative unless a source is named.
This is the overview for the calculations section. Related guides: how to read your electricity bill, LPG cylinder cost per month, PMUY subsidy, PNG versus LPG, PM Surya Ghar and net metering and the checklist to reduce your bill.
Step 1: units
Units = present reading − previous reading (× the meter multiplying factor, which is 1 for ordinary home meters). Check that the billing period is the usual length. If the bill says "average" or "provisional", the units are estimated; see why bills suddenly go up.
Example 1: Delhi, 350 units, 3 kW
Rates: DERC domestic schedule (FY 2020-21 schedule, continued by the FY 2021-22 order).
| Step | Calculation | Amount |
|---|---|---|
| Energy, 0–200 units | 200 × ₹3.00 | ₹600.00 |
| Energy, 201–350 units | 150 × ₹4.50 | ₹675.00 |
| Energy charge | ₹1,275.00 | |
| Fixed charge | 3 kW × ₹50 | ₹150.00 |
| PPAC/FPPAS (illustrative 17.9%, close to the June 2026 level DERC allowed BRPL) | 17.9% × ₹1,425 | ₹255.08 |
| Additional surcharges in the DERC schedule (8% deficit recovery + 7% pension trust) | 15% × ₹1,425 | ₹213.75 |
| Gross bill (before electricity tax) | ₹1,893.83 | |
| Delhi subsidy, 201–400 band (50%, capped at ₹800 a month) | 50% of gross | −₹946.92, limited to −₹800 |
| Payable (illustrative) | ₹1,093.83 |
The 8% and 7% surcharges are listed in note 7 of the DERC tariff schedule for FY 2021-22 and apply to the fixed and energy charges only; the municipal electricity tax is left out here, so check its rate on your bill. Two things to notice. First, the cap matters: half of ₹1,894 is ₹947, more than the ₹800 monthly cap in the Delhi government's subsidy order. Second, the subsidy exists only if the household opted in. Without it, the household pays the gross bill. How the scheme treats surcharges, and whether the cap is applied exactly as here, should be checked against the DISCOM's subsidy notice; our example shows the method.
Example 2: Delhi, 180 units, 2 kW
| Step | Calculation | Amount |
|---|---|---|
| Energy | 180 × ₹3.00 | ₹540 |
| Fixed | 2 × ₹20 | ₹40 |
| PPAC and other items (illustrative 25% combined) | 25% × ₹580 | ₹145 |
| Gross | ₹725 | |
| Subsidy (up to 200 units: full) | −₹725 | |
| Payable | ₹0 |
The same household at 201 units would lose the full subsidy and fall to 50%. Units close to 200 deserve attention in summer.
Example 3: Tamil Nadu, 500 units in two months
Rates: TNERC Suo-motu Order No. 6 of 2025 dated 30 June 2025, effective 1 July 2025, LT-IA domestic, Commission-determined, bi-monthly. Fixed charge: nil. The order provides for a CPI-based revision from 1 July 2026; check whether the rates have changed.
| Slab (two months) | Units | Rate | Amount |
|---|---|---|---|
| 0–400 | 400 | ₹4.95 | ₹1,980 |
| 401–500 | 100 | ₹6.65 | ₹665 |
| Commission tariff | 500 | ₹2,645 |
The Government of Tamil Nadu subsidises domestic consumers, so the bill shows a government subsidy line and a lower amount payable. From 10 May 2026, according to reports of G.O. (Ms) No. 50 and TNERC's follow-up subsidy order, households using up to 500 units in two months get 200 units free and those above 500 units get 100 units free. We do not quote the payable figure because the subsidised rates are set by government policy, not by the TNERC order; read them from your bill.
Example 4: Tamil Nadu, 800 units in two months
| Slab | Units | Rate | Amount |
|---|---|---|---|
| 0–400 | 400 | ₹4.95 | ₹1,980 |
| 401–500 | 100 | ₹6.65 | ₹665 |
| 501–600 | 100 | ₹8.80 | ₹880 |
| 601–800 | 200 | ₹9.95 | ₹1,990 |
| Commission tariff | 800 | ₹5,515 |
Average: ₹5,515 ÷ 800 = ₹6.89 per unit, against ₹5.29 at 500 units. The last 300 units cost ₹2,870, or about ₹9.57 each. In a hot two-month cycle, cutting 100 units would save ₹995 at the Commission rate.
Example 5: Tamil Nadu above 500 units, in the calculator
The electricity bill calculator applies the TNERC Order No. 6 of 2025 slabs telescopically: each block of units is charged at its own rate, including for households above 500 units. Enter 1,100 units for a two-month cycle and it shows:
| Slab (two months) | Units | Rate | Amount |
|---|---|---|---|
| 0–800 (as in Example 4) | 800 | ₹5,515 | |
| 801–1,000 | 200 | ₹11.05 | ₹2,210 |
| Above 1,000 | 100 | ₹12.15 | ₹1,215 |
| Commission tariff | 1,100 | ₹8,940 |
The average is ₹8,940 ÷ 1,100 = about ₹8.13 per unit, well below the ₹12.15 top rate. For Delhi, use the slab-by-slab method in Examples 1 and 2; the calculator covers only the Tamil Nadu schedule.
Common calculation mistakes
| Mistake | Effect |
|---|---|
| Applying the top slab rate to all units | Overstates the energy charge |
| Forgetting the fixed charge | Understates the bill, especially at higher loads |
| Using last month's surcharge rate | Surcharges change monthly |
| Comparing a two-month bill with a monthly one | Doubles the apparent increase |
| Ignoring the subsidy cap or threshold | Wrong payable amount near 200 or 400 units in Delhi |
| Not checking the billing period length | A 40-day bill is not comparable to a 30-day one |
When the numbers do not match
If your recalculation differs from the bill by more than rounding, list each line with your figures and ask the DISCOM to explain the difference in writing. Use the bill check and dispute checklist and, if needed, the CGRF route.
Frequently asked questions
Why is my calculated bill slightly different from the DISCOM's?
Rounding, pro-rating of slabs for billing periods that are not exactly a month, and the order in which surcharges and duty are applied can cause small differences. Large differences usually mean a different rate, base or units.
Is the surcharge calculated before or after subsidy?
Normally the gross bill, including surcharge, is calculated first, and the subsidy is applied after. The subsidy notice for your state sets the exact treatment.
Can I use these examples for Maharashtra or Karnataka?
Use the same method with your own SERC's schedule. We have not quoted MSEDCL or Karnataka ESCOM rates because we could not confirm the schedules in force.
Sources and where to check
- TNPDCL — TNERC T.O. No. 6 of 2025 and online bill calculator
- Delhi Electricity Regulatory Commission — Delhi tariff schedule and PPAC orders
- Delhi Government Power Department — subsidy scheme notices
- BSES Delhi — DERC tariff schedules and the Delhi subsidy leaflet as published by the DISCOM
- Ministry of Power — billing rights under the Electricity (Rights of Consumers) Rules
