Tariffs, Price Drivers and 2026 Rules
Telescopic slab tariff explained - how electricity units are charged in India
What telescopic and non-telescopic slabs mean, how monthly and bi-monthly billing changes your rate, and how to work out the cost of extra units.
Under a telescopic slab tariff, each block of units you use is charged at the rate for that block only. The first 200 units might be charged at one rate, the next 200 at a higher rate, and so on; when you cross into a higher slab, only the units above the threshold pay the higher rate, and the earlier units keep their lower rates. Most Indian SERCs use telescopic slabs for domestic consumers. The practical consequence is simple: your extra units are always charged at your highest slab, so your average rate per unit is lower than the rate printed against your top slab.
Part of how electricity tariffs are set in India.
Telescopic slabs with a real schedule
The Delhi domestic schedule applied by DERC (set in the FY 2020-21 tariff schedule and kept unchanged in the FY 2021-22 order) is a clear example:
| Monthly units | Energy charge (₹/unit) |
|---|---|
| 0–200 | 3.00 |
| 201–400 | 4.50 |
| 401–800 | 6.50 |
| 801–1,200 | 7.00 |
| Above 1,200 | 8.00 |
Energy charge for 550 units, slab by slab:
| Slab | Units in slab | Rate | Amount |
|---|---|---|---|
| 0–200 | 200 | ₹3.00 | ₹600 |
| 201–400 | 200 | ₹4.50 | ₹900 |
| 401–800 | 150 | ₹6.50 | ₹975 |
| Total | 550 | ₹2,475 |
The average is ₹2,475 ÷ 550 = ₹4.50 per unit, even though the top slab rate is ₹6.50. If the same household used 50 more units, the extra 50 would cost 50 × ₹6.50 = ₹325, not 50 × ₹4.50.
Non-telescopic and threshold structures
Some states have used, at different times, structures where crossing a threshold changes the rate for all units or moves the consumer to a different sub-category. A simplified illustrative example:
| Structure | 240 units cost |
|---|---|
| Telescopic: 0–200 at ₹4, 201+ at ₹6 | 200 × 4 + 40 × 6 = ₹1,040 |
| Non-telescopic: all units at ₹6 once above 200 | 240 × 6 = ₹1,440 |
In the non-telescopic case, 40 extra units add ₹640 to the bill instead of ₹240. Subsidy schemes often work like a threshold too: in Delhi, the full subsidy applies only up to 200 units a month, and above that only a partial subsidy applies. Read your state's tariff order for words such as "telescopic", "for the entire consumption" or "category shall be decided by", and see the free-power scheme guide for how subsidy thresholds behave.
Monthly versus bi-monthly billing
Some DISCOMs read meters every month, others every two months. Tamil Nadu's domestic LT-IA tariff, for example, is set in bi-monthly slabs. TNERC Suo-motu Order No. 6 of 2025 (dated 30 June 2025, effective 1 July 2025) lists these Commission-determined energy charges for domestic consumers, with no fixed charge:
| Units in two months | Units per month equivalent | Energy charge (₹/unit) |
|---|---|---|
| 0–400 | 0–200 | 4.95 |
| 401–500 | 201–250 | 6.65 |
| 501–600 | 251–300 | 8.80 |
| 601–800 | 301–400 | 9.95 |
| 801–1,000 | 401–500 | 11.05 |
| Above 1,000 | Above 500 | 12.15 |
The order sets this single table for all domestic consumption, and the slabs are applied telescopically: a household using 600 units in two months pays ₹4.95 on the first 400, ₹6.65 on the next 100 and ₹8.80 only on the last 100 (₹3,525 in all at Commission rates). These are the rates before the Tamil Nadu government's subsidy, which lowers what domestic consumers actually pay; from 10 May 2026 the free allowance was reported as 200 units per cycle for households up to 500 units and 100 units above that. The order provides for a CPI-linked revision from 1 July 2026, so confirm whether a newer schedule now applies.
Two points matter with bi-monthly billing:
- Slabs scale with the period. A correctly applied bi-monthly slab is roughly double the monthly one, so you are not penalised for the longer period.
- Seasonal peaks bunch together. If April and May are both hot months with heavy fan and cooler use, the two-month bill captures both, and the units above 400 are charged at the steep upper rates.
If a DISCOM that normally bills monthly issues one bill covering a longer period, for example after a missed reading, ask whether the slabs have been pro-rated for the number of days. Many supply codes require this. See why electricity bills suddenly go up.
How to work out the cost of an extra appliance
- Find your usual monthly units from the last 12 bills.
- Estimate the appliance's monthly units (watts × hours per day × 30 ÷ 1,000).
- Add them to your usual units and see which slab or slabs they fall into.
- Multiply the extra units by the slab rates they occupy.
Illustrative example (Delhi schedule): a household at 380 units adds a 2,000 W immersion heater for 1 hour a day in winter, about 60 units a month. 20 units fall at ₹4.50 (up to 400) and 40 units at ₹6.50, adding ₹350 in energy charge, plus any FPPAS and duty. Air-conditioner and geyser running costs are covered in depth by specialist guides; the method is the same.
Common misreadings
| What people assume | What actually happens |
|---|---|
| "My rate is ₹6.50, so 500 units cost ₹3,250" | Only the units above 400 pay ₹6.50; the total is ₹2,150 under the Delhi schedule |
| "Bi-monthly billing doubles my slab cost" | Slabs should be doubled for two months; check the bill shows bi-monthly slab limits |
| "Cutting 50 units saves 50 × my average rate" | It saves 50 × your top slab rate, which is more |
| "Slabs include the fixed charge" | Fixed charges are separate and based on sanctioned load |
Try your own Tamil Nadu units with the electricity bill calculator, which applies the TNERC slabs one block at a time, and see the full bills in electricity bill calculation worked examples.
See also: the fixed part of the bill and slab structures in four states.
Frequently asked questions
Is every state's domestic tariff telescopic?
Most are, but not all states and not all categories. Some apply a different tariff once consumption crosses a threshold, and subsidy schemes often have hard thresholds. The tariff schedule in your SERC's order will say how the slabs apply.
Why does my bill show "units in slab" lines?
That breakdown is the telescopic calculation. Each line shows the units charged at one rate. Adding the lines gives the energy charge before surcharges, duty and subsidy.
My DISCOM changed from bi-monthly to monthly billing. Will I pay less?
If the slab limits are also halved, the total over a year should be similar. You may pay less in seasons where one month is heavy and the next is light, because the heavy month no longer pulls the light month's units into higher slabs.
Where can I find my state's slab table?
In the tariff schedule annexed to your SERC's tariff order, usually also on the DISCOM's website and printed on the back of the bill.
Sources and where to check
- TNPDCL — TNERC tariff order T.O. No. 6 of 2025 and the domestic LT-IA slabs
- Delhi Electricity Regulatory Commission — Delhi tariff orders and schedules
- Central Electricity Authority — annual report on tariffs and electricity supply charges across states
- Ministry of Power — Electricity (Rights of Consumers) Rules on billing
