How to Calculate Electricity Bill: Formula & Examples
To calculate your electricity bill, multiply the units you consumed by your state's slab rate, add the fixed charge for your sanctioned load, then add electricity duty and any fuel adjustment charge. The short version is: Total bill = (units × slab rate) + fixed charge + electricity duty + FPPCA. The catch most people miss is that the per-unit rate is not one number. It rises in steps as you use more, so the simple "units × one rate" sum almost always comes out lower than the bill that actually arrives.
This guide shows the full method with real Indian figures, then walks through two worked examples so you can check your own bill line by line.
At a glance
Item | What it means | Typical value (verify with your DISCOM) |
|---|---|---|
1 unit | 1 kilowatt-hour (kWh): a 1,000 W appliance run for 1 hour | — |
Units consumed | Current meter reading minus previous reading | Family of 4: 200 to 400 units/month |
Energy charge | Units billed across progressive slabs | ₹3 to ₹10+ per unit by state and slab |
Fixed charge | Monthly charge per kW of sanctioned load, payable even at zero use | ₹40 to ₹130+ per month |
Electricity duty | State tax on the subtotal | 4% to 16% |
FPPCA / FAC / FSA | Fuel and power purchase cost adjustment | ₹0.50 to ₹1.50 per unit |
National average domestic tariff sat around ₹5.5 to ₹7.2 per unit in FY 2025-26, with Tamil Nadu's subsidised slabs near the bottom and Maharashtra's upper slabs above ₹10. Treat every rupee figure here as illustrative and confirm your own slab from your latest bill (verify at publish).
How electricity bill is calculated, step by step
Your meter counts cumulative units since the day it was installed. The number you pay for is the difference between this month's reading and last month's. Everything else on the bill is built on that one figure.
Here is the method:
- Find units consumed. Current reading − previous reading. If the meter shows 04,810 now and 04,230 last month, you used 580 units.
- Split units across slabs. India uses a telescopic (progressive) tariff. The first block is cheap; each higher block costs more.
- Multiply each block by its rate and add them up. This is your energy charge.
- Add the fixed charge. It is charged per kW of sanctioned load, so a 2 kW connection pays twice the per-kW rate every month, even in a month you used nothing.
- Add electricity duty (a percentage of the subtotal) and FPPCA (a per-unit fuel adjustment that moves up or down each cycle).
Two households on the same street with identical consumption can still get different bills, because their sanctioned load, tariff category, or state duty differs.
Electricity bill calculation formula
The formula in full:
Total bill = Σ(units in each slab × that slab's rate) + (sanctioned load in kW × fixed charge per kW) + electricity duty + FPPCA ± other levies
The "Σ" matters. Writing it as units × single rate is the single most common reason a self-calculated bill comes out wrong. Crossing one slab boundary does not re-price all your units in most states; only the units inside the higher block are charged at the higher rate. A few states apply the higher rate to the whole consumption, so check your DISCOM's rule.
Worked example A: a 580-unit summer bill
Using an illustrative four-slab structure (substitute your own state's numbers):
Slab | Units in slab | Rate (illustrative) | Charge |
|---|---|---|---|
0 to 150 | 150 | ₹5.50 | ₹825 |
151 to 300 | 150 | ₹6.00 | ₹900 |
301 to 500 | 200 | ₹7.00 | ₹1,400 |
501 to 580 | 80 | ₹8.00 | ₹640 |
Energy charge | 580 | — | ₹3,765 |
Now add the rest, for a 3 kW sanctioned load:
- Fixed charge: 3 kW × ₹110 = ₹330
- Subtotal: ₹3,765 + ₹330 = ₹4,095
- Electricity duty at 5%: ₹205
- FPPCA at ₹0.80/unit × 580 = ₹464
- Total ≈ ₹4,764
Your effective rate is ₹4,764 ÷ 580 = ₹8.21 per unit, well above the ₹5.50 first-slab rate. That gap is the slab effect doing its work.
Worked example B: the same home in winter (250 units)
Slab | Units | Rate | Charge |
|---|---|---|---|
0 to 150 | 150 | ₹5.50 | ₹825 |
151 to 250 | 100 | ₹6.00 | ₹600 |
Energy charge | 250 | — | ₹1,425 |
Add ₹330 fixed + 5% duty (₹88) + FPPCA (₹200) = ₹2,043, or ₹8.17 per unit. Less than half the summer total, because the costly upper slabs never get touched. This is why summer bills feel disproportionate: the air conditioner does not just add its own units, it pushes the whole bill into the expensive blocks.
Why your bill jumps even when habits do not change
Three causes account for most "my bill is wrong" complaints, and none of them is an error:
- Longer billing cycle. A 33-day cycle bills three extra days at the same rates. More units, same habits.
- Slab creep from one appliance. A 1.5-tonne AC run 8 hours a day adds roughly 250 units a month, often enough to cross into a higher slab.
- FPPCA swing. When the DISCOM's fuel cost rises, this line goes up on its own. It is a standard regulatory mechanism, not a mistake.
Before disputing a bill, check the cycle dates, the units, your consumer category, and whether an FPPCA or adjustment line appears.
How to calculate electricity bill online without doing the maths
You do not have to compute slabs by hand. To calculate electricity bill online, use your DISCOM's official portal or a state-specific calculator: enter your state, your units (or current and previous meter readings), and your sanctioned load, and it applies the current slabs, fixed charge, duty and surcharges for you. Always cross-check the calculator's total against your paper bill; a large gap points to either a billing error or a charge you had not accounted for. Our companion electricity bill calculator walks through this with appliance-level inputs.
Honest limits of any bill calculation
- Slabs change yearly. State commissions revise tariffs, usually between April and June. A number that was right last year may not be right now.
- Calculators estimate. Subsidies (Tamil Nadu's free units, Karnataka's Gruha Jyothi, Delhi's rebate) and category rules vary, and not every tool models them correctly.
- Estimated readings distort one month. If a meter could not be read, the DISCOM estimates, then reconciles against an actual reading later, which can spike a single bill.
Who this guide suits
Strong fit | Marginal fit | Not the right page |
|---|---|---|
Households checking a bill that looks high | Tenants wanting a rough monthly budget | Industrial HT consumers (demand charges, power factor penalties differ) |
Anyone sizing a solar system or inverter to cut bills | Small shops on commercial tariff | Anyone needing their exact state slab table (go to your DISCOM) |
Cutting the bill, not just calculating it
Once you can see your effective per-unit rate, the savings logic becomes obvious: every unit you stop drawing from the grid in an upper slab is the most expensive unit to lose, so it saves the most. Two practical levers:
- Rooftop solar with net metering. A 3 kW system generates roughly 360 to 450 units a month and can offset most of a typical home's consumption, with surplus exported to the grid for credit. Under PM Surya Ghar: Muft Bijli Yojana the central subsidy is up to ₹78,000 for systems up to 3 kW (verify current slabs and state top-ups at publish). Solar units stored in an Adwin solar battery (UEST series) keep cutting your billed units after sundown instead of pulling from the grid at the upper slab rate.
- Backup that does not inflate the bill. An Adwin inverter battery covers outages without adding daytime grid load. Pair it with an Adwin home inverter or solar PCU for a system that runs on stored or solar power during peak-rate hours.
FAQs
How is electricity bill calculated in India?
It is calculated by splitting your consumed units across progressive tariff slabs, multiplying each block by its rate, then adding a fixed charge based on your sanctioned load, electricity duty (a state tax), and a fuel adjustment charge. The total divided by your units gives your real effective per-unit rate.
What is the electricity bill calculation formula?
Total bill = the sum of (units in each slab × that slab's rate) + (sanctioned load in kW × fixed charge per kW) + electricity duty + FPPCA. The slab-by-slab sum is the part people skip, which is why hand estimates run low.
How do I calculate electricity bill from units consumed?
Find units consumed (current meter reading minus previous), apply your state's slab rates block by block for the energy charge, then add fixed charge, duty and fuel surcharge. A 580-unit bill at the illustrative rates above works out to about ₹4,764.
Can I calculate electricity bill online for free?
Yes. Your DISCOM's official website and several state-specific calculators let you enter your units or meter readings and return a slab-wise bill. They are free and need no login. Always compare the result against your actual bill.
What is 1 unit of electricity?
One unit is one kilowatt-hour: the energy a 1,000-watt appliance uses in one hour. A ceiling fan uses roughly one unit over eight hours; a 1.5-tonne AC uses about 1.5 to 2 units per hour.
Why is my electricity bill higher than units × rate?
Because of the progressive slab system plus fixed charge, duty and fuel surcharge. Higher consumption pushes units into costlier slabs, so your effective rate climbs above the first-slab rate even though your habits did not change.
Are fixed charges payable if my house is locked all month?
Yes. Fixed charges are billed on your sanctioned load to cover network and metering costs, regardless of whether you consume a single unit. A locked home still gets a fixed-charge bill.
Does rooftop solar reduce the calculated bill?
Yes. Solar generation offsets grid units, and net metering credits surplus export against import. Because it removes units from your most expensive upper slabs first, the rupee saving per unit is larger than the first-slab rate suggests.
Bottom line
Calculating an electricity bill is slab maths plus three add-ons (fixed charge, duty, fuel surcharge), not a single multiplication. Once you know your effective per-unit rate, you can judge whether solar, an inverter battery, or simply trimming peak-slab usage is worth it for your home.
