How this instrument works
An LED bulb and an old incandescent bulb can put out the same amount of light while drawing very different amounts of power, because they convert electricity to light at very different efficiencies — LEDs are dramatically more efficient per lumen than incandescent filaments. That wattage gap, multiplied out across a bulb's actual daily runtime and a full year, is where real savings show up: a few watts difference sounds small per hour, but 60 fewer watts running 5 hours a day for 365 days adds up to a meaningful chunk of a household's electricity bill.
This calculator runs that math directly: it takes the wattage difference between the old and new bulb, multiplies by daily hours of use and days per year, and divides by 1,000 to convert watt-hours into kilowatt-hours (kWh) — the unit electricity is actually billed in. Multiplying that annual kWh figure by your electricity rate gives the dollar savings.
The result scales with how much the bulb is actually used — a rarely-used closet light swapped to LED saves far less per year than a porch light or living room lamp left on for hours daily, even with the identical wattage difference. Enter your bulb's real daily usage, not just its wattage, for an accurate annual figure.
- Enter Old bulb wattage (W) — the wattage of the bulb you're replacing.
- Enter New LED wattage (W) — the wattage of its LED replacement.
- Enter Hours used per day — how long that specific fixture is actually turned on daily, on average.
- Enter Electricity rate ($/kWh) — your utility's price per kilowatt-hour, found on a recent electric bill.
- Read Energy saved (kWh/year) and Cost saved ($/year) for the annual energy and dollar savings from making the swap.
Worked example — swapping a 60W incandescent for a 9W LED
A classic 60-watt incandescent bulb in a living room lamp, used about 5 hours a day, is replaced with a 9-watt LED equivalent — a very common real-world upgrade, since a roughly 9W LED is widely sold as the direct replacement for 60W-incandescent brightness. At a $0.16 per kWh electricity rate, Energy saved (kWh/year) comes to (60 − 9) x 5 x 365 / 1000 = 93.075 kWh.
Cost saved ($/year) follows as 93.075 x $0.16 = $14.892, or roughly $14.89 a year from that single bulb. Multiply that by every similarly-used incandescent bulb still in a home, and the combined annual savings from a full LED conversion adds up considerably faster than any single bulb suggests on its own.
Questions
Why does a 9-watt LED replace a 60-watt incandescent bulb?
Because LEDs convert electricity into visible light far more efficiently than an incandescent filament does, so an LED needs far fewer watts to produce the same brightness (measured in lumens). This site's luminous-efficacy figures put LEDs at roughly 75-plus lumens per watt versus an incandescent bulb's much lower efficacy, which is exactly why a 9W LED and a 60W incandescent can put out comparable light despite the large wattage gap.
Does this calculator account for the cost of buying the LED bulb itself?
No — it calculates ongoing electricity savings only, not the upfront purchase cost or the payback period. To estimate payback time, divide the LED bulb's purchase price by the Cost saved ($/year) figure this calculator returns; the result is roughly how many years of use it takes for the electricity savings to cover the bulb's cost.
How much does daily usage actually affect the savings?
Substantially — the savings scale directly with hours used per day, so a bulb left on for 8 hours daily (like a porch light) saves proportionally more per year than an identical wattage swap on a closet light used for 10 minutes a day. Enter your fixture's real average daily usage rather than a rough guess for an accurate annual figure.
Does this include savings from the LED bulb lasting longer than incandescent?
No — this calculator covers electricity cost only. LED bulbs also typically last many times longer than incandescent bulbs, which reduces how often you need to buy and install a replacement, but that reduced-replacement-frequency saving isn't included in the Cost saved ($/year) figure here.
Where do I find my electricity rate in dollars per kWh?
It's listed on a recent electric utility bill, usually as a per-kWh charge, sometimes broken into multiple line items (supply, delivery, taxes) that combine into an effective total rate. If your bill only shows a total dollar amount and total kWh used, divide the dollar total by the kWh total to get your effective rate for this calculator's Electricity rate field.