How it works
Every bulb's electricity use is its wattage × the hours it is on. Swapping a 60 W incandescent for a 9 W LED that gives the same light (about 800 lumens) cuts that by 85%. The calculator prices the difference at your electricity rate for every bulb you replace.
It also counts the bulbs you no longer buy: an incandescent lasts about 1,000 hours, so a bulb used 3 hours a day needs replacing every year, while an ENERGY STAR LED is rated for 15,000 hours or more. Dividing the LED's price by the yearly saving gives the payback time.
Most incandescent bulbs can no longer be sold in the US, UK, EU and Australia, so this mainly applies to bulbs still in use, plus halogen and CFL bulbs.
The formula
kWh saved per bulb = (old watts − LED watts) × hours a day × 365 ÷ 1,000 energy saving = kWh saved × price per kWh bulbs avoided = hours a year ÷ old bulb life × old bulb price payback (months) = LED price ÷ (energy saving + bulbs avoided) × 12
Worked example
One 60 W incandescent bulb replaced by a 9 W LED costing $2.50, on 3 hours a day at 18.2¢ per kWh.
| Step | Working | Result |
|---|---|---|
| Electricity saved | 51 W × 1,095 h ÷ 1,000 | 55.8 kWh a year |
| Energy saving | 55.8 × $0.182 | $10.16 |
| Replacement bulbs avoided | 1,095 ÷ 1,000 × $1.50 | $1.64 |
| Saving a year | $11.81 | |
| Payback | $2.50 ÷ $11.81 × 12 | 2.5 months |
| Over the LED's life | 13.7 years × $11.81 − $2.50 | $159 |
Ten bulbs save about $118 a year. In the UK, at 26.32p per kWh, the electricity saving alone is about £14.70 per bulb a year.
Frequently asked questions
How much money do LED bulbs save?
About $10.16 a year in electricity for each 60 W incandescent replaced, if it is on 3 hours a day at the US average price, plus the replacement bulbs you no longer buy. Bulbs left on longer save proportionally more.
Is it worth replacing CFLs with LEDs?
The saving is small: a 13 W CFL uses only 4 W more than a 9 W LED. It is usually best to replace CFLs as they fail, unless they are on for many hours a day.
How many watts does an LED bulb use?
A 60 W equivalent (800 lumens) uses about 8 to 10 W, a 75 W equivalent about 11 to 13 W, and a 100 W equivalent about 14 to 17 W. Check lumens, not watts, when comparing brightness.
How long do LED bulbs last?
ENERGY STAR LED bulbs are rated for 15,000 hours or more: about 14 years at 3 hours a day. Heat shortens their life, so bulbs in enclosed fittings may fail sooner unless rated for them.
Sources
- ENERGY STAR, why choose ENERGY STAR light bulbs (rated life of certified LEDs).
- US Department of Energy, LED lighting.
- Default prices: US average residential price, EIA 2026 forecast (checked Oct 2026); Ofgem price cap unit rate, 1 Oct – 31 Dec 2026, Direct Debit (VAT on electricity is 0% until 31 Mar 2027).
Estimates are for planning only and are not financial advice. Get written quotes before you buy.