What this calculator does
Every lighting upgrade comes down to one comparison: how many watts the old bulb burned versus the new one, multiplied by how long the light is actually on. This tool runs that comparison for a whole batch of bulbs at once, converts it to dollars at your electricity rate, and then projects it across ten years — including the incandescents you won’t have to keep rebuying.
The result is the number that matters when you’re standing in the hardware aisle deciding whether the LED two-pack is worth the extra couple of dollars. Spoiler: it almost always is.
How to use it
- Bulbs you’re replacing. Count the sockets you actually plan to switch — start with the lights that stay on longest: kitchen, living room, porch.
- Old vs. LED wattage. The defaults (60W → 9W) match a standard 800-lumen bulb. For a 100W-equivalent, try 100W → 15W; for a 40W, 40W → 6W.
- Hours on per day. Be realistic — a porch light on dusk-to-dawn runs 10–12 hours; a closet light maybe 15 minutes. The longer a bulb runs, the bigger the payoff.
- Electricity rate. Find the “price per kWh” on your utility bill. The US average is about $0.18; some states are well north of $0.30.
The formula, in plain English
Energy cost is just power × time × price. A bulb’s power is its wattage; a kilowatt-hour is 1,000 watts running for an hour, which is the unit your utility bills you in:
The percentage saved is simply how much smaller the LED’s wattage is: a 9W LED replacing a 60W bulb uses 85% less, full stop, no matter how long it’s on. Runtime only changes the dollar size of that 85%.
Don’t forget the bulbs you stop buying
Energy is only half the story. An incandescent is rated for about 1,000 hours; an LED for around 25,000. Over a decade of normal use you’ll buy roughly two dozen incandescents per socket — versus one LED. The 10-year total in the readout folds in that avoided spending, which is why it’s noticeably larger than ten times the annual energy figure.
Getting the most out of the switch
- Match lumens, not watts. Look for ~800 lumens to replace a 60W bulb, ~1,600 for a 100W.
- Pick the right color temperature: 2700K (warm white) for living spaces, 4000K+ for garages and workspaces.
- Prioritize high-runtime fixtures first — the savings are proportional to hours, so the porch and kitchen beat the guest closet every time.
- Look for the ENERGY STAR mark for verified lifespan and light quality.
Frequently asked
How much does one LED bulb save per year?
Replacing a single 60-watt incandescent used 3 hours a day with a 9-watt LED saves roughly $9–$10 a year at average US electricity prices. It sounds small, but a typical home has 40–50 sockets — switch the ones you use most and the total climbs into three figures fast.
Why do LEDs use so much less energy?
An incandescent bulb makes light by heating a filament until it glows, and about 90% of the energy escapes as heat rather than light. An LED produces the same brightness electronically with almost no wasted heat, so a 9-watt LED matches the ~800 lumens of a 60-watt incandescent — about 85% less power.
Are LEDs worth it given the higher purchase price?
Yes. An LED costs a couple dollars more up front but lasts around 25,000 hours versus 1,000 for an incandescent — roughly 25 bulbs’ worth — and pays back the difference in energy in a matter of months. The calculator’s 10-year figure includes those avoided replacement purchases.
Do smart LED bulbs save the same amount?
On energy, yes — a smart LED draws about the same watts as a standard LED when on. The trade-off is a small standby draw (often 0.3–0.5W) to keep the radio listening, which our Phantom Load Calculator can account for. The upside is scheduling and dimming, which cut runtime further.