Electricity Bill Calculator

How an electricity bill is actually built

When to use this: checking a bill that looks wrong, working out what you owe before it arrives, comparing two tariffs properly, or deciding whether an efficiency measure pays for itself.

Almost every bill calculator online models the same equation: units times rate. Real bills have at least three more parts, and each of them changes the answer materially.

1. The energy charge — units consumed multiplied by the rate. This is the part everyone models.
2. The standing charge — a fixed fee per day, owed whether you consume anything or not.
3. The rate structure — flat, tiered by consumption, or varying by time of day.
4. Tax — applied to the sum of the two charges, not to energy alone.

Put together: (kWh × rate + days × standing charge) × (1 + tax). At 900 kWh, 0.25 per unit, 0.6 a day for 30 days and 5% tax, that is (900 × 0.25 + 30 × 0.6) × 1.05 = 255.15.

The standing charge is the part everyone forgets

It goes by many names — standing charge, daily supply charge, service charge, fixed charge, customer charge, meter rent. It covers the cost of maintaining the network and reading the meter, and it is charged per day regardless of consumption.

This has a consequence that is easy to state and easy to miss: your bill has a floor. At 0.6 a day, a 30-day month costs 18.90 before you switch anything on. No amount of turning lights off gets below it.

And because that floor is fixed, it makes up a larger share of a small bill than a large one — which means the less electricity you use, the more you pay per unit:

At 0.25 per kWh with a 0.6 standing charge, a 50 kWh month works out at 0.640 per unit — 156% above the headline rate. A 3,000 kWh month pays 0.269, barely above the advertised price.

This is why comparing tariffs on the per-kWh rate alone is a mistake. A tariff at 0.22 per kWh with a 1.00 daily standing charge and one at 0.28 with no standing charge cross over at a specific consumption level; below it the second is cheaper, above it the first. Work out the effective rate at your usage and compare those.

Tiered and slab tariffs: only the excess pays the higher rate

Under a tiered tariff — also called block rates, slab rates or an increasing block tariff — consumption is divided into bands and each band has its own price. Common in California, much of India, parts of Australia and many municipal utilities.

The error that keeps appearing in hand calculations is charging the whole month at whichever rate you reached. You do not. Each block is priced separately, and you only pay the top rate on the portion above the threshold.

Take 0.32 up to 350 kWh, 0.41 up to 1050 kWh, then 0.55. A 900 kWh month:

Charging all 900 kWh at the tier 2 rate would give 369.00 — an overstatement of 31.50, or 9%.

Average rate versus marginal rate

The bill above averages 0.3750 per kWh. But the next kWh costs 0.41, because that is the block you are sitting in.

The distinction decides whether efficiency measures are worth it. Cutting 100 kWh from that month saves 100 × 0.41 = 41.00 — not 100 × 0.3750. Savings always come off the top block first, so on a tiered tariff a heavy user gets a better return on the same reduction than a light one.

Time-of-use tariffs reward moving load, not reducing it

A time-of-use tariff prices the same kWh differently by hour: expensive during the late afternoon and evening peak, cheap overnight. The spread is often three or four to one.

Whether it saves you money depends entirely on what share of your consumption falls in the peak window. With a 0.40 peak and 0.15 off-peak rate against a flat 0.25:

The break-even sits at 40% — below that a time-of-use tariff wins, above it you lose. Most households land near 35–45% without deliberate effort, which is why switching to time-of-use and changing nothing else often makes bills worse.

The loads worth shifting, in order of how much they move the number: EV charging, electric hot water, laundry, dishwasher, pool pump. An EV alone can shift several hundred kWh a month into the cheap window, which is why time-of-use tariffs and EVs are so often recommended together.

Reading your meter correctly

• Digital meters: record the digits before the decimal point. Ignore digits after it, and any figure in a red box or shown in a different colour — those are tenths.
• Dial meters: read left to right. Where a pointer sits between two numbers, take the lower one. If a pointer is directly on a number, check the dial to its right: if that reads 0–1, use the number; if it reads 8–9, use the number below.
• Two-rate meters: economy or off-peak meters show two registers, usually marked "low"/"normal" or "R1"/"R2". Read both and apply the correct rate to each.
• Rollover: if the current reading is lower than the previous one, the meter has passed its maximum. Add the meter's full range — normally 100,000 — to the current reading before subtracting.

What normal consumption looks like

Wide variation is normal, and it is driven overwhelmingly by whether heating and hot water are electric.

European and UK homes sit far lower — typically 2,700 to 3,500 kWh a year — because heating and hot water are almost always gas. Comparing a UK figure with a US one without accounting for that is comparing two different things.

Why your bill came in higher than you calculated

• The standing charge was left out. The most common cause by a wide margin, and it accounts for a fixed amount you cannot find in the consumption figures.
• The period was longer than you assumed. A "monthly" bill may cover 28 to 31 days; quarterly bills run 90 or more. Both the standing charge and any tier thresholds scale with it.
• The previous reading was estimated. If the last bill was estimated low, the correction lands on this one. Compare the reading type on both bills — actual readings are usually marked "A" and estimates "E".
• You crossed into a higher tier. On a block tariff the extra units cost more than the average rate you are used to seeing.
• The rate changed mid-period. Bills spanning a price change are split, and the average rate you compute from the total will match neither published figure.

Reducing the bill, in order of effect

Multiply by your marginal rate, not your average one, and work down from the largest loads. Our appliance wattage chart gives the annual consumption of around 58 household appliances, which is where to start.

1. Heating and cooling — typically 40–50% of an all-electric home's usage. A degree on the thermostat is worth more than every standby device combined.
2. Hot water — 10–20%. Lowering the tank thermostat and insulating it are cheap and permanent.
3. EV charging — often the single largest appliance load. Shift it, do not cut it.
4. Standby — worth attacking selectively. A games console left in rest mode costs roughly 85 times what a phone charger does. Unplugging chargers is the most repeated advice and nearly the least effective.