Which appliances actually drive your electricity bill

Electricity bills in most Indian homes have a shape. They're tolerable from November to February, start climbing in March, and peak in May when the AC runs all evening. People notice the peak and assume everything is to blame: the fridge, the TV left on standby, the phone chargers. Usually it's one or two appliances. The trick is to put numbers on each of them.

Watts × hours is the whole formula

A unit on your bill is one kilowatt-hour (kWh): 1,000 watts running for one hour. So for any appliance, monthly units = watts × hours per day × days ÷ 1,000.

A 75 W ceiling fan running 10 hours a day for 30 days uses 75 × 10 × 30 ÷ 1,000 = 22.5 units. A 9 W LED bulb on for 6 hours a day uses 9 × 6 × 30 ÷ 1,000 = 1.62 units. A geyser rated at 2,000 W, used half an hour each morning, uses 2,000 × 0.5 × 30 ÷ 1,000 = 30 units. That half hour costs more than a fan running all day.

Watts are on the rating label, usually on the back or underside. Hours are where people go wrong. Most of us underestimate how long the AC runs and overestimate how long the TV does. If you're not sure, note the times for a few days.

The appliance electricity cost calculator lets you list each appliance with its watts, quantity, hours and days, and shows units, monthly cost and each one's share of the total.

Why the fridge's nameplate overstates its use

The fridge is on 24 hours a day, so it looks like an obvious suspect. But the compressor doesn't run continuously. It runs until the inside is cold, switches off, and starts again when it warms up. The wattage on the rating plate is what it draws while running, not its average.

Say the plate says 120 W. Treat that as constant and you'd get 120 × 24 × 30 ÷ 1,000 = 86.4 units a month. Now look at the BEE star label, which gives an annual energy figure in kWh per year. Suppose it says 250. That's 250 ÷ 12 = about 20.8 units a month, or an average draw of 250 ÷ 8,760 hours × 1,000 = about 28.5 W. A quarter of what the nameplate suggests.

Real use will be a little higher than the label in an Indian summer, with a hot kitchen and the door opened often, but the label is a far better starting point than the plate. In the calculator, enter the average watts worked out from the label and 24 hours a day.

The AC is usually the answer

Take a split AC with a rated input of 1,500 W running 8 hours a night through May. That's 1,500 × 8 × 31 ÷ 1,000 = 372 units for the month from one appliance. In many homes that's more than everything else combined.

Two things change the AC's number a lot. The first is its efficiency, which is what the star rating describes. A higher star rating means more cooling for each unit of electricity. The label also prints an estimated annual consumption, based on a standard number of hours of use per year, which is useful for comparing two models even if your hours are different.

The second is the thermostat. An inverter AC slows its compressor once the room reaches the set temperature, so it doesn't draw full rated power all night. Setting 24 °C or 25 °C instead of 18 °C means the compressor spends much more of the night running slow. A fixed-speed AC cycles on and off instead, but the same logic applies: a higher set point means less time on. Combined with a ceiling fan, a few degrees higher usually feels about the same and costs noticeably less. Check the filters too; clogged filters make every model work harder.

Standby and the small stuff

Standby is real, but small. Say a set-top box, a TV, a Wi-Fi router and a microwave clock together draw 20 W around the clock. That's 20 × 24 × 30 ÷ 1,000 = 14.4 units a month. At ₹7 a unit it's ₹100.80. Worth switching off at the wall if it's easy, but not where the big money is. The set-top box is often the biggest of these, since many stay fully on when "off".

Things that are easy to forget: the water pump or booster pump, the iron, the mixer, the washing machine's heater if you use hot washes, the microwave and induction hob, and an inverter battery charging after power cuts. If your calculated total comes out well below your bill, one of these is usually missing.

Reading a DISCOM bill

Bills vary by state and DISCOM, but most residential bills have the same building blocks.

• Units consumed: the current meter reading minus the previous one.
• Energy charge: the units priced through slabs. In most places the slabs are telescopic, meaning the first block of units is billed at the lowest rate, the next block at a higher rate, and so on.
• Fixed or demand charge: a monthly amount based on your sanctioned load or connection type, payable even if you use nothing.
• Electricity duty and other levies: a state duty, often a percentage of the energy charge, plus fuel or power purchase cost adjustments in some states.
• Subsidy or rebate: some states give free or subsidised units below a threshold, shown as a credit.

Here's a hypothetical bill to make it concrete. The slabs are ₹3 per unit for the first 100 units, ₹5 for 101–200, and ₹7 for 201–400. Fixed charge is ₹120 a month and duty is 5% of the energy charge. You used 350 units.

Energy charge: 100 × 3 = ₹300, plus 100 × 5 = ₹500, plus 150 × 7 = ₹1,050, totalling ₹1,850. Duty at 5% is ₹92.50. With the ₹120 fixed charge, the bill is 1,850 + 92.50 + 120 = ₹2,062.50.

Working out your own average tariff

For the calculator you need one rate per unit. Take the energy charge on your bill and divide by units consumed. In the example, 1,850 ÷ 350 = ₹5.29 per unit. If you want duty included, add it first: (1,850 + 92.50) ÷ 350 = ₹5.55. Enter the fixed charge separately, since it doesn't change with use.

Use a bill from the same season you're modelling. A winter bill might sit almost entirely in the cheap slabs, which makes the average rate look low and summer costs look smaller than they are.

There's one subtlety I'd keep in mind. The average rate tells you what your total costs. It does not tell you what you save by cutting use, because cuts come off the top slab first. In the example, running that 1,500 W AC one hour less each day saves 1,500 × 1 × 30 ÷ 1,000 = 45 units. Those units come out of the ₹7 slab, not at the ₹5.29 average, so the saving is 45 × 7 = ₹315 a month plus the duty on it, not 45 × 5.29 = ₹238. You'd still be in the same slab at 350 − 45 = 305 units. Some DISCOMs bill differently, for example charging all units at a higher rate once you cross a threshold, so check the tariff schedule for your state and category on your DISCOM's website.

Putting your home's list together

Open the electricity cost calculator with your last summer bill in hand. Replace the sample appliances with your own, using label watts for most things and the annual kWh figure for the fridge. Enter your average rate and fixed charge. Then compare the calculator's total units with the units on your bill. If they're within about 10%, your list is good enough to act on. If not, something is missing or the hours are off.

Once they match, the share column usually makes the decision obvious. If you're renovating and planning new ACs or a bigger geyser, run them through the calculator first and check your sanctioned load; the renovation budgeting guide explains why a load upgrade belongs in the budget. Then change one thing, like the AC set point or the geyser timer, and compare next month's units with this month's.