Three tenants each used 120 units. You read all three sub-meters, added them up, and got 360 units. The DISCOM bill for the main meter says 360 units too. The readings agree perfectly and the money still does not: bill the tenants individually and you collect Rs 1,770 against a bill of Rs 2,590.
Nobody tampered with anything. The Rs 820 hole is what happens when you split a slab tariff by arithmetic that slabs do not support. Here is where the money goes, and the one splitting method that always closes to zero.
Table of contents
- The gap, in one table
- Why slabs do not decompose
- The method that always balances
- It also fixes unequal usage
- Common load is a separate problem
- Compare against the energy charge, not the total
- Write the method down before the first bill
- FAQ
- Conclusion
- Sources
The gap, in one table
Every figure below uses one illustrative three-block tariff: Rs 4.50 for the first 100 units, Rs 7.00 for the next 100, Rs 9.00 after that. Your state commission publishes the real blocks and revises them, so read the slab table printed on your own bill before you settle anything. The structure is what matters here, and the structure is the same almost everywhere in India.
| Consumption | How it is charged | Total | Effective rate |
|---|---|---|---|
| 120 units | 100 x 4.50 + 20 x 7.00 | Rs 590 | Rs 4.92 |
| 360 units | 100 x 4.50 + 100 x 7.00 + 160 x 9.00 | Rs 2,590 | Rs 7.19 |
One tenant at 120 units pays Rs 4.92 per unit. The building at 360 units pays Rs 7.19 per unit for the same electricity. Multiply the single-tenant bill by three and you get Rs 1,770, which is 46% short of what the utility charged.
Why slabs do not decompose
The slab discount attaches to the connection, not to the person. Your building has one connection, so it gets one set of cheap first-100 units, and the tenants have already spent it collectively by unit 100.
Bill each tenant alone and you hand out that cheap block three times over. Three lots of 100 units at Rs 4.50 is 300 discounted units the utility never granted, because on a single meter only the first 100 units of the whole building are priced at Rs 4.50. Units 200 through 360 sit in the Rs 9.00 block, and no individual tenant reading of 120 ever reaches it.
That is the whole gap. It is a structural property of a progressive tariff, not a rounding error, and it grows as consumption rises: the deeper the main meter reaches into the expensive block, the wider the hole in your collection.
The method that always balances
Stop pricing tenants against the slab table. Derive one rate from the bill you actually received:
flat rate = total energy charge on main bill / total units on main meter
= 2590 / 360
= Rs 7.1944 per unitThen charge every tenant that rate:
| Tenant | Units | Amount |
|---|---|---|
| A | 120 | Rs 863.33 |
| B | 120 | Rs 863.33 |
| C | 120 | Rs 863.33 |
| Total | 360 | Rs 2,590.00 |
The collection closes to the paisa, because you divided the real bill instead of rebuilding an imaginary one. Each tenant pays Rs 273 more than a naive slab calculation would suggest, and that Rs 273 is their honest share of the expensive block their own usage helped reach.
Do not round the derived rate to two decimals before multiplying. Rs 7.19 across 360 units loses about Rs 1.60 against the real bill, and someone has to eat it. Keep four decimals, or divide the money instead of the rate.
Once you have the rate, the Indian Electricity Calculator turns each tenant's two meter readings into a payable amount, which is the part you repeat every month. Feed it the derived rate rather than a slab rate off the bill.
It also fixes unequal usage
Equal usage is the easy case. The method matters more when consumption differs, because that is when a wrong split looks defensible.
Same 360 units on the main meter, distributed as 60, 120 and 180:
| Units | Own-slab bill | Proportional share |
|---|---|---|
| 60 | Rs 270 | Rs 431.67 |
| 120 | Rs 590 | Rs 863.33 |
| 180 | Rs 1,010 | Rs 1,295.00 |
| 360 | Rs 1,870 | Rs 2,590.00 |
Own-slab billing leaves Rs 720 uncollected here. The proportional method closes exactly and keeps the ordering intact: the tenant who used three times as much pays three times as much.
The heavy user is not being punished. They are carrying three times the share of a rate their consumption is largely responsible for, which is the closest thing to fair that a single-connection tariff allows.
Common load is a separate problem
Corridor lights, the water pump, a lift, the motor for an overhead tank. None of it appears on any tenant's sub-meter, and all of it appears on the main meter.
Add 40 units of common load to the same building and the main meter reads 400 units, billing Rs 2,950. The tenants recorded 360 between them. Those 40 unattributed units sit at the top of the tariff, in the Rs 9.00 block, so they cost Rs 360 rather than the Rs 288 an average-rate calculation would suggest.
Settle common load as its own line, not by inflating the per-unit rate. Split it equally per flat, or by floor area if the flats differ a lot in size. Rs 360 over three flats is Rs 120 each. Sub-meters also miss line losses in the cabling between the main board and each unit, which is a real but usually small residue.
If electricity is one of several shared heads, the Shared Expense Split Calculator handles the whole set in one pass instead of one spreadsheet per bill.
Compare against the energy charge, not the total
The derived rate must come from the energy charge line on the bill, not the amount payable. A DISCOM bill also carries items that have nothing to do with consumption:
Fixed or demand charges are billed against your sanctioned load in kW. A locked flat that used zero units still gets one. Meter rent is a flat monthly amount where the utility owns the meter. Electricity duty and state cesses are applied on top of the tariff. The fuel and power purchase adjustment surcharge moves month to month with what the utility paid for power.
Divide the total payable by units and your rate absorbs all of that, which quietly charges tenants for a fixed charge that belongs to the connection. Pull the energy charge line out first, derive the rate from it, then decide separately how the fixed heads are shared. Splitting them equally per flat is the usual answer.
Subsidy credits deserve a check too, since they can make the net bill much lower than the gross, and passing on the gross while pocketing the credit is a real dispute waiting to happen.
Write the method down before the first bill
The arithmetic is not what makes these arguments ugly. The timing is. A method agreed before anyone has seen a bill reads as fair; the same method proposed after a Rs 2,590 bill arrives reads as an attempt to shift Rs 820.
Four lines in the rental agreement or a WhatsApp message both parties keep:
The per-unit rate is derived monthly by dividing the main meter's energy charge by its total units. Common-area load is the difference between the main meter and the sum of sub-meters, split equally per flat. Fixed charges, meter rent and duty are split equally per flat. Readings are taken on the same date each month, with photos.
That last one prevents more disputes than the rest combined. A reading taken four days late in an air-conditioned month moves real money, and a photo of the display settles in seconds what memory argues about for a week.
For a tenancy that ends mid-cycle, the Move-In / Move-Out Meter Settlement tool handles the part-period case, where the next official bill covers two different occupants.
FAQ
Why is the main meter bill higher than the sum of the sub-meters? Because a slab tariff charges per connection. The cheap first block belongs to the building once, but billing each tenant separately hands it out once per tenant. At 120 units each, three tenants total Rs 1,770 while the 360-unit main bill is Rs 2,590.
What is the correct per-unit rate to charge a tenant? The main bill's energy charge divided by the main meter's total units. On a Rs 2,590 bill for 360 units that is Rs 7.1944 per unit. Charging a slab rate off the bill undercollects.
Is it legal for a landlord to charge more than the DISCOM rate per unit? Charging above the derived average is a common complaint and several state regulators cap what a landlord may recover from a tenant, so check your state's rules. The proportional method never exceeds the real bill, which is what makes it defensible.
Should tenants pay the fixed charges too? Those attach to the connection and the sanctioned load, not to consumption, so folding them into the per-unit rate charges heavy users for a bill that does not vary with usage. Split them equally per flat as a separate line.
How do I handle corridor lights and the water pump? Treat the difference between the main meter and the sum of the sub-meters as common load and split it separately. It sits in the top slab, so 40 units on this tariff costs Rs 360, or Rs 120 per flat across three.
Does the gap get bigger with higher consumption? Yes. The gap is the value of the discounted blocks you duplicated plus the top-block units no individual reading reaches, so it widens as the main meter climbs further into the expensive slab.
Can I just divide the total bill equally between flats? Only if usage is genuinely similar. Equal division ignores the sub-meters you installed to avoid exactly that, and it overcharges the tenant who travels for work.
Do prepaid smart meters remove this problem? Separate metered connections per flat remove it, because each connection then gets its own slab treatment. A single connection with sub-meters keeps the gap regardless of whether the main meter is prepaid.
Conclusion
A slab tariff cannot be taken apart and reassembled. Bill the tenants against the slab table and you will always collect less than you paid, by a margin that grows with the building's consumption.
Divide the energy charge by total units, apply that one rate to everybody, settle common load and fixed charges as their own lines, and agree the whole thing in writing before the first bill lands. The collection then closes to the paisa every month, with no argument about who reached which slab.
For the monthly part, the Indian Electricity Calculator takes two readings and your derived rate and returns the amount payable with the units shown, so both parties can check the same number.
Sources
- Slab arithmetic in this post was computed from the illustrative three-block tariff stated in the first section (Rs 4.50 / Rs 7.00 / Rs 9.00 in 100-unit blocks), not taken from any one state's tariff order. Verify the blocks against your own bill.
- Telescopic slab billing, fixed charges, meter rent, electricity duty and fuel surcharge line items are standard components of Indian DISCOM domestic bills; the slab table on your bill and your state commission's current tariff order are the authoritative figures.
