Show the formula and working
This free Christmas lights cost calculator works out how much electricity your Christmas lights use and what they cost to run per hour, per day and over the whole festive season, for households in the UK, Ireland and Europe. It also compares LED strings with older, more power hungry sets, so you can see what switching saves, using your own unit rate in pounds or euros.
Quick answer: A Christmas lights cost calculator multiplies watts by hours and days, divides by 1,000 for kWh and multiplies by your unit rate. Four 5 W LED strings on 6 hours a day for 31 days use 3.72 kWh, about 93p at an example 25p per kWh.
What Is a Christmas Lights Cost Calculator?
A Christmas lights cost calculator is a tool that converts the power rating of your festive lights and the hours you use them into energy in kWh and a running cost.
The formula in plain words: multiply the number of sets by the watts per set for the total power. Multiply by the hours on per day and divide by 1,000 to get kilowatt hours per day. Multiply by the number of days for the season’s energy, then by your electricity price per kWh for the cost. The watts are printed on the light set’s label or its plug in transformer.
How Do You Use the Christmas Lights Cost Calculator?
- Enter the Number of light sets and the Watts per set from the label. If your sets differ, enter their average, or run the tool once for each type.
- Enter the Hours on per day and Days switched on.
- Enter your Electricity price per kWh from your bill.
- Set Compare with watts per set of to an older set’s wattage, or 0 to hide the comparison.
- Read the result and open “Show the formula and working” to see the power, kWh and cost per hour, day and season.
How Much Do Christmas Lights Cost to Run?
Indoor LED Christmas lights usually cost pennies for the whole season: a 5 W string on 6 hours a day for 31 days uses 0.93 kWh, about 23p at 25p per kWh. Large outdoor displays and older filament sets cost far more. The table uses 6 hours a day for 31 days at an example 25p per kWh, so enter your own rate in the tool.
| Lights (example wattage) | Total watts | kWh per season | Cost per season at 25p |
|---|---|---|---|
| 1 indoor LED string, 5 W | 5 | 0.93 | 23p |
| 4 indoor LED strings, 5 W each | 20 | 3.72 | 93p |
| 10 LED strings, 5 W each | 50 | 9.30 | £2.33 |
| 1 older filament string, 40 W | 40 | 7.44 | £1.86 |
| 4 older filament strings, 40 W each | 160 | 29.76 | £7.44 |
| Outdoor display, 200 W in total | 200 | 37.20 | £9.30 |
Are LED Christmas Lights Cheaper to Run?
Yes. LED strings use a fraction of the power of older filament bulb strings for a similar display, so they cost far less to run. In the default example, four 5 W LED sets cost 93p for the season against £7.44 for four 40 W filament sets, a saving of £6.51. LEDs also run cooler, which reduces the risk of scorching decorations. Check your own sets’ labels, because wattages vary.
How Can You Cut the Cost of Christmas Lights?
The cheapest ways are a plug in timer so lights are only on when people will see them, LED sets instead of filament ones, and switching off overnight. Battery sets avoid mains wiring but replacing batteries can cost more than mains power. For other gadgets left on around the house, the standby power cost calculator shows what they add up to.
Are Christmas Lights Safe to Leave On Overnight?
It is safest to switch Christmas lights off when you go to bed or leave the house. Check sets for damaged cables and loose bulbs before use, use outdoor rated sets and sockets outside, plugged into a socket protected by an RCD, and buy from reputable sellers. Do not overload extension leads with large displays, as one 13 A lead carries about 2,990 W in total. Electrical Safety First publishes festive safety advice.
Worked Example: Four LED Strings Through December
Example: four indoor LED light strings rated at 5 W each, on for 6 hours a day for 31 days, at an example price of 25p per kWh, compared with 40 W filament sets. These are the tool’s default inputs.
- Total power: 4 x 5 W = 20 W.
- Energy per day: 20 x 6 / 1,000 = 0.12 kWh, costing 3p.
- Season: 0.12 x 31 = 3.72 kWh, costing 93p.
- Filament comparison: 4 x 40 x 6 x 31 / 1,000 = 29.76 kWh, costing £7.44, so the LEDs save £6.51.
The current unit rate under the energy price cap is shown on Ofgem’s energy price cap page, but your own tariff may differ, so use the rate on your bill. For any other appliance, try the electricity cost calculator.
Christmas Lights Cost Calculator FAQs
How do I work out how much my Christmas lights cost?
Multiply the watts by the hours on, divide by 1,000 for kWh, and multiply by your price per kWh. A 20 W display on 6 hours a day uses 0.12 kWh, about 3p a day at 25p per kWh.
How many watts do Christmas lights use?
It varies widely. Many indoor LED strings use only a few watts, while older filament strings and large outdoor displays can use tens or hundreds of watts. The exact figure is printed on the label or the plug transformer.
Is it cheaper to leave Christmas lights on or turn them off?
Turning them off is always cheaper, because lights use no energy when off and switching on uses no extra burst worth counting. A timer that switches them off overnight cuts both cost and safety risk.
Do Christmas lights add much to an electricity bill?
LED lights usually add very little: the default four string example costs 93p for the whole of December. Big outdoor displays with hundreds of watts, inflatables and older filament sets add more, so run the calculator with your own figures.
Are solar Christmas lights free to run?
Solar sets cost nothing to run from the mains, but in UK and northern European winters they get little sun, so they may be dim or switch off early. They suit decorative outdoor lighting rather than a bright display.
Can I plug lots of light sets into one extension lead?
LED strings use so little power that several are usually fine, but the total must stay under the lead’s rating, about 2,990 W for a 13 A UK lead. Never daisy chain extension leads, and use outdoor rated equipment outside.
Checked October 2026. Sources: Ofgem, Energy price cap, Wikipedia, Kilowatt-hour, Electrical Safety First. The 25p rate is an example only.