Everyday Life⏱ 5 min read
How to Calculate Your Electricity Bill Before It Arrives
Understanding how electricity is priced and calculated lets you predict bills, identify high-cost appliances, and know instantly if a bill looks wrong. Here's the complete guide.
Electricity bills contain more information than most people realise — and understanding the maths means you can estimate costs in advance, track your usage, and spot billing errors before you pay them.
The Core Calculation
Cost = Units used (kWh) × Unit rate (p/kWh) + Standing charge
kWh = kilowatt-hours = the standard unit of electricity consumption
1 kWh = using 1,000 watts (1 kW) for 1 hour
Unit rate (2025 England/Wales price cap): ~24.5p/kWh
Standing charge: ~61p/day (regardless of usage)
Converting Appliance Power to kWh
kWh used = Watts ÷ 1,000 × Hours used
Example: 2,000W kettle, used 5 times/day for 2 min each
= 2,000 ÷ 1,000 × (5 × 2/60)
= 2 × 0.167 = 0.333 kWh/day
= 0.333 × 24.5p = 8.2p/day = ~£2.50/month
Monthly Cost of Common Appliances
ApplianceTypical UsageMonthly Cost (24.5p/kWh)
Electric shower (9kW)8 min/day~£35
Tumble dryer (2.5kW)5 cycles/week, 45 min~£17
Dishwasher (1.2kW)1 cycle/day, 60 min~£8.80
Washing machine (2kW)5 cycles/week, 45 min~£13
Fridge-freezer (150W)24hr/day~£27
60" TV (100W)4 hrs/day~£3
LED bulb (8W)5 hrs/day~£0.30
Desktop PC (200W)5 hrs/day~£7.35
EV charging (7kW home)8 hrs/week~£54
Reading Your Smart Meter / Bill
Units used = Current reading − Previous reading (in kWh)
Bill calculation:
Units used: 350 kWh
Unit rate: 24.50p = £0.245
Standing charge: £0.61/day × 30 days = £18.30
Electricity cost: 350 × £0.245 = £85.75
Standing charge: £18.30
Subtotal: £104.05
VAT (5% on domestic electricity): £5.20
Total: £109.25
Economy 7 and Smart Tariffs
Economy 7 (and similar Economy 10) tariffs offer a lower "off-peak" rate for 7 hours overnight, with a higher daytime rate. Worthwhile only if you can shift significant usage (storage heaters, overnight EV charging, dishwasher / washing machine on timer) to the cheap period.
Economy 7 example (2025 approximate):
Off-peak rate: ~9p/kWh (midnight–7am)
Peak rate: ~33p/kWh (7am–midnight)
Standing charge: ~62p/day
Worth it if: 40%+ of usage is in off-peak hours.
Break-even: roughly shifting 1,500+ kWh/year to off-peak.
How to Reduce Your Bill
In order of impact: the electric shower and tumble dryer dominate most household bills. Reducing shower time from 10 minutes to 6 minutes saves ~£175/year. Air-drying laundry instead of tumble drying saves ~£200/year. These two changes alone can save more than all LED lighting upgrades combined.