Electricity Bill Slab Estimator
Estimate your bill using slab tariffs, fixed charges and duty — the way discoms bill.
Electricity is not billed at one rate. Consumption moves through slabs, each dearer than the last, and then fixed charges, fuel surcharge and duty are added on top. This estimator reproduces that structure so you can check a bill or predict the effect of running an air conditioner for another month.
Consumption and tariff
Result
Fill in the fields above and your result will appear here.
What the Electricity Bill Slab Estimator does
Slab tariffs mean the first hundred units cost far less than the four hundredth. That is why the average rate on your bill is always lower than the cost of the next unit you consume — and why the marginal rate is the right number when deciding whether an appliance is worth running.
Every state regulator publishes its own tariff order and most revise it annually. The slabs loaded here are a sample shape, not any particular discom's tariff, and should be replaced with the figures printed on your own bill.
How to use this tool
- Enter the units consumed, from your meter reading or the bill itself.
- Replace the sample slabs with your own. Each row is the upper limit of a slab and the rate that applies within it.
- Leave the last slab at a very high limit so it acts as the top band.
- Add fixed charges, meter rent, fuel surcharge and electricity duty exactly as your bill shows them.
- Compare the total with your actual bill. If they differ, a component is missing — the slab table shows where.
Formula and method
Energy charge = Σ (Units within each slab × That slab's rate)
Fuel charge = Units × Fuel surcharge per unit
Subtotal = Energy + Fuel + Fixed charge + Meter rent
Duty = Subtotal × Duty %
Total bill = Subtotal + Duty − Subsidy
Average rate = Total ÷ Units
Marginal rate = Rate of your highest slab × (1 + Duty %)
Worked example
Example: 320 units on a four-slab tariff
| First 100 units at ₹4.00 | ₹400 |
| Next 100 units at ₹5.50 | ₹550 |
| Next 120 units at ₹7.00 | ₹840 |
| Energy charge | ₹1,790 |
| Fixed charge and meter rent | ₹120 |
| Duty at 5% | ₹95.50 |
| Total bill | ≈ ₹2,005 |
The average is ₹6.27 a unit, but the next unit costs ₹7.35 including duty. Any decision about running one more appliance should use the second figure.
What your result means
The marginal rate is the number that matters for decisions. Deciding whether to run an air conditioner an extra hour should use it, not the average.
Fixed charges are unavoidable. On a low bill they can be a large share of the total, which is why reducing consumption never reduces the bill proportionally.
If your estimate is well below your actual bill, the usual causes are a missing fuel surcharge, a higher sanctioned-load fixed charge, or arrears carried forward from a previous month.
Important considerations
- Slab structures differ substantially between states, and several apply the highest slab rate to all units once a threshold is crossed, rather than only to units above it. Read your tariff order carefully.
- Fixed charges usually depend on sanctioned load. If your sanctioned load is higher than you need, reducing it lowers the fixed charge permanently.
- Fuel and power purchase cost adjustments change monthly in several states and can add meaningfully to a bill.
- Some states offer free or subsidised units for domestic consumers up to a threshold. Enter any such rebate in the subsidy field.
- Rooftop solar with net metering changes the calculation entirely, since exported units offset imported ones.
- A sudden jump in a bill with no change in usage often indicates a faulty meter or an estimated reading. Compare consecutive meter readings before disputing.
Limitations of this tool
- It models a standard progressive slab structure. Telescopic and non-telescopic tariffs differ, and some states apply the top rate to the whole consumption once a threshold is crossed.
- Time-of-day tariffs, which are being introduced for some consumer categories, are not modelled.
- Arrears, adjustments, security deposit interest and one-off charges that appear on real bills are not included.
Frequently asked questions
How is an electricity bill calculated in India?
Units are charged progressively across slabs, then fixed charges, meter rent and any fuel surcharge are added, and electricity duty is applied on the total. Subsidies, where applicable, are deducted at the end.
Why is my average rate lower than the slab rate?
Because the earlier slabs are cheaper. Your first hundred units might cost ₹4 while your last cost ₹8, so the average sits between them. The marginal rate is what applies to any additional consumption.
What are fixed charges on an electricity bill?
A monthly charge based on your sanctioned load, payable regardless of how much you consume. It covers the cost of maintaining the connection. Reducing your sanctioned load, if it is higher than you need, reduces it permanently.
Where do I find my tariff slabs?
On your bill, usually itemised under energy charges, and in full in your state regulator's tariff order published on the discom website. Use those figures rather than any default.