How to Calculate Electricity Bill from Units (kWh)

Guides · Calculator · Updated 2026

Your electricity bill arrives every month, but the jump from ₹400 to ₹800 can feel mysterious if you don’t understand slab‑based billing. Unlike a simple unit‑price × consumption model, most Indian state boards charge different rates for different consumption blocks — the more you use, the higher the per‑unit cost becomes. This guide explains how to read your meter, understand kWh, and calculate your bill using a flexible slab calculator.

What is a unit (kWh) and how is it measured?

A “unit” on your bill is 1 kilowatt‑hour (kWh) — the energy consumed by a 1,000‑watt appliance running for one hour. A ceiling fan (75W) running 8 hours uses 0.6 kWh. Your meter records cumulative kWh, and the monthly consumption is the difference between two consecutive readings. Knowing your approximate daily usage helps you predict the bill before it arrives.

Understanding slab‑based billing

Slabs are consumption brackets. For example, the first 100 units may cost ₹3.5 each, the next 100 units ₹4.5 each, and so on. Once you cross into a higher slab, only the units in that slab are charged at the higher rate — not your entire consumption. However, your average per‑unit cost increases, which is why the bill feels disproportionately higher when you use just a few extra units.

Example generic slab table (editable):

From (units)	To (units)	Rate (₹/unit)
0	100	3.5
101	200	4.5
201	300	6.0
301	above	7.5

Then fixed charges and a tax/duty percentage are added to get the final bill.

Step-by-step: estimate your electricity bill

Open the Electricity Bill Calculator tool.
Enter the total units consumed (from your meter or last month’s bill). Edit the slab table if your state board uses different rates.
Enter the fixed charge (if any) and the duty/tax percentage (often 5%).
The tool shows your energy charge, fixed charge, tax, total bill, and a per‑slab breakdown — so you can see exactly how much each bracket contributed.

💡 Tip: To lower your bill without sacrificing comfort, focus on the highest‑slab appliances — air conditioners and water heaters. Even a small reduction in peak‑hour usage can save you hundreds because it reduces the units charged at the most expensive rate.

Worked example: 250 units with the sample slabs

First 100 units × ₹3.5 = ₹350. Next 100 units (101–200) × ₹4.5 = ₹450. Remaining 50 units (201–250) × ₹6 = ₹300. Energy charge = ₹1,100. Add fixed charge ₹50 → subtotal ₹1,150. Add 5% tax = ₹57.50 → total bill = ₹1,207.50. If the same household uses 310 units, those extra 10 units are charged at the highest slab ₹7.5, adding ₹75 plus tax, making the bill jump noticeably.

Frequently Asked Questions

Why does my bill suddenly double even though I didn’t use much more?

You likely crossed into a higher slab, and also the fixed charges or fuel adjustment charges may have kicked in. Check your unit count against the slab boundaries.

Can I change the slab rates in the calculator?

Yes, the calculator’s slab table is fully editable. Find your state electricity board’s latest tariff order online and plug in the exact rates.

What is a fuel surcharge or adjustment charge?

It’s an additional per‑unit charge that varies monthly based on coal or gas prices. You can add it as a separate flat per‑unit rate in the duty/tax field if you know the amount.

Is 1 unit = 1 kWh the same everywhere in India?

Yes, a unit always equals 1 kWh. The pricing varies by state and slab, but the unit definition is universal.

Is it free and private?

Yes — the tool runs entirely in your browser, free, with no sign‑up and nothing uploaded to a server.

Try the Electricity Bill Calculator