You open your TNEB bill and it's noticeably higher than last time — even though it doesn't feel like you used much more. Before you assume a faulty meter, it's worth understanding how Tamil Nadu actually charges for electricity. Once you see how the slab (telescopic) system works, the "jump" makes sense — and you'll know exactly what to do about it.
"Telescopic" means your units are billed in blocks, and each higher block costs more per unit. Crucially, only the units inside each block are charged at that block's rate — crossing a threshold does not retroactively make your whole bill expensive. Here are the current domestic (residential) bimonthly rates:
| Units (bimonthly) | Rate per unit |
|---|---|
| 0 – 200 | FREE (Govt. scheme) |
| 0 – 400 | ₹4.95 |
| 401 – 500 | ₹6.65 |
| 501 – 600 | ₹8.80 |
| 601 – 800 | ₹9.95 |
| 801 – 1000 | ₹11.05 |
| Above 1000 | ₹12.15 |
Rates per TNERC T.O.No.6 of 2025 + the May 2026 Government subsidy (200 units free). TNEB bills are bimonthly — every two months.
Two things happen together. First, in hot months your usage genuinely climbs — an AC or extra fan running longer quietly adds units. Second, those extra units land in a higher-priced block. A unit that would have cost ₹4.95 in the lowest block costs ₹8.80 once you're in the 501–600 range. Same appliance, nearly double the marginal cost.
Here's the honest math, so there's no myth: going from 490 to 510 bimonthly units adds only about ₹155 in energy charges — not a shocking figure by itself. The real "shock" bills come from bigger jumps, like 400 units one cycle to 650 the next, where hundreds of extra units pile into the higher blocks.
If your bimonthly consumption stays at or under 200 units (about 100 units a month), your bill is ₹0 under the current Tamil Nadu scheme. Many small households sit right around this line — which is exactly where a little awareness saves the most.
Instead of guessing, you can watch your bill build up block by block. We built a couple of free tools for this:
📊 TNEB Bill Calculator — enter your units and see the exact slab-by-slab breakdown, plus a live Slab Guard that warns you when you're close to a costlier block.
🏠 Sharing a flat? Roommate Bill Splitter — split the bill fairly by shared load and each person's AC hours, not just "divide by number of people".
If your usage truly hasn't changed and the bill still spikes, it may be a metering or wiring issue — a faulty meter, or current leaking to earth through damaged wiring. In that case, raise it with TNEB. Our TNEB complaint guide walks through how to log a grievance properly.
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