What an LED savings calculator tells you
Switching from an incandescent, halogen or CFL bulb to an LED cuts the wattage that produces the same brightness by 80–90%. This calculator turns that wattage gap into real money: it works out the annual electricity cost of running your old bulb, the cost of running the LED that replaces it, and the difference — your annual saving — for one bulb or for a whole house full of them. It also projects the saving over ten years, the typical LED lifespan.
How LED savings are calculated
The running cost of any bulb is a single, instant calculation — there is no compounding and no time value. First convert watts to kilowatt-hours, then multiply by your electricity rate:
annual kWh = (watts ÷ 1000) × hours per day × days per year × bulbs
annual cost = annual kWh × rate per kWh
The saving is simply the difference between the two bulbs’ annual costs:
annual savings = old bulb cost − LED cost
Sign-aware: if the LED you enter draws more than the old bulb, the saving comes out negative — the tool shows that rather than hiding it, so the comparison is always honest.
Why the wattage gap is so large
Incandescent bulbs waste roughly 90% of their energy as heat and only 10% as light. LEDs flip that ratio, so a 9W LED produces the same ~800 lumens as a 60W incandescent. Compare bulbs by lumens (brightness), not watts, and replace at the equivalent wattage below:
| Brightness | Incandescent | Halogen | LED |
|---|---|---|---|
| ~250 lm | 25 W | 18 W | 3 W |
| ~450 lm | 40 W | 29 W | 5 W |
| ~800 lm | 60 W | 43 W | 9 W |
| ~1100 lm | 75 W | 53 W | 12 W |
| ~1600 lm | 100 W | 72 W | 15 W |
Worked example
A single 60W incandescent replaced by a 9W LED, run 5 hours a day all year at the US-average rate of $0.1387/kWh — generated by the same engine that powers the calculator above.
| Metric | 60W old bulb | 9W LED | Saved |
|---|---|---|---|
| Annual energy | 109.5 kWh | 16.4 kWh | 93.1 kWh |
| Annual cost | $15.19 | $2.28 | $12.91 |
| 10-year cost | $151.88 | $22.78 | $129.10 |
The LED uses 16.4 kWh against the incandescent’s 109.5 kWh — an 85% energy cut — saving about $12.91 a year, or roughly $129 across a ten-year LED lifespan, from a single bulb.
Payback period: how quickly does an LED pay for itself?
The energy savings alone usually repay the higher purchase price of an LED within a few months. The formula is straightforward:
payback (months) = (LED price − old bulb price) ÷ (annual savings ÷ 12)
Based on the default scenario above — 60W incandescent to 9W LED, 5 hours/day, $0.1387/kWh — annual savings are $12.91/year. At that saving rate, even a premium LED recoups its extra cost within a year:
| Scenario | Extra upfront cost | Payback period |
|---|---|---|
| Budget LED, standard incandescent | $1.25 | ~1 months |
| Mid-range LED, standard incandescent | $3.25 | ~3 months |
| Premium LED, standard incandescent | $6.25 | ~6 months |
| Mid-range LED, halogen equivalent | $1.50 | ~1 months |
After payback, the remaining LED lifespan — typically 15,000–25,000 hours, or 8–15 years at 5 h/day — is pure savings. A $4 LED that pays back in 4 months still has more than 14 years of saving ahead of it.
CO2 savings from LED lighting
Lower energy use also means fewer carbon emissions. Every kWh not consumed avoids the CO2 that would have been generated to produce it:
CO2 avoided (kg/year) = kWh saved per year × grid emissions factor (kg CO2/kWh)
The US national average grid emissions factor is approximately 0.386 kg CO2 per kWh (EPA eGRID data). For the default scenario above, switching one 60W bulb to a 9W LED saves 93.1 kWh/year, avoiding roughly 35.9 kg CO2 per year. Replacing ten bulbs across a household avoids over 359 kg CO2 annually — equivalent to taking a small car off the road for several weeks.
Your grid may differ. The UK grid factor is around 0.207 kg CO2/kWh (DEFRA), while coal-heavy grids can exceed 0.7 kg CO2/kWh. Use your region's published factor for a country-specific estimate. The CO2 saving shown here uses the US EPA average.
What this calculator does not include
To keep the figures honest, the calculator models electricity running cost only:
- It excludes the bulb purchase price and the savings from an LED’s longer life and fewer replacements.
- It assumes a single flat per-kWh rate — no tiered, time-of-use or demand charges, taxes or standing fees.
- It assumes constant daily use and equivalent brightness between the two bulbs.
- It ignores heat-load effects: incandescent waste heat can raise summer cooling or offset winter heating.
Enter the rate from your own bill and your real daily hours for the most accurate result. The national-average default is illustrative only.
Frequently asked questions
How much can I save annually by switching from a 60W incandescent to a 9W LED bulb?+
At the US national average electricity rate of around $0.14/kWh and 5 hours of daily use, a single bulb swap from 60W to 9W saves roughly $12–$13 per year. Over a 10-year LED lifespan that exceeds $120 in electricity savings alone, before accounting for the many incandescent replacements you avoid.
What electricity rate should I use in the calculator?+
Check your electricity bill for the cents-per-kWh rate. The US national residential average is around $0.14/kWh (EIA data), but rates range from under $0.10/kWh in Louisiana to over $0.25/kWh in California and Hawaii. The default in this calculator is $0.1387/kWh as a reasonable starting point — replace it with your actual rate for an accurate result.
How do I calculate the energy cost of a light bulb?+
Multiply the bulb’s wattage by the hours used, divide by 1,000 to convert to kilowatt-hours (kWh), then multiply by your electricity rate. For example: a 60W bulb used 5 hours/day for 365 days uses (60 ÷ 1000) × 5 × 365 = 109.5 kWh/year. At $0.1387/kWh that costs about $15.19 per year.
Do LED bulbs really save money if they cost more to buy?+
Yes, in almost every scenario. A typical 9W LED replacement costs $2–$5 and lasts 15,000–25,000 hours, while the 60W incandescent it replaces costs under $1 but lasts only 1,000 hours — meaning you need 15–25 incandescent bulbs over the same period. Add the energy savings of around $12/year per bulb and the LED pays back its purchase price within a few months.
How many kWh does a light bulb use per year?+
Annual kWh = (watts ÷ 1,000) × hours per day × days per year. A 60W bulb at 5 hours/day uses 109.5 kWh/year. A 9W LED under the same conditions uses only 16.4 kWh/year — an 85% reduction in energy consumption.
What is the payback period for switching to LED lighting?+
Payback period = (LED purchase price − one incandescent price) ÷ annual energy savings. For a $4 LED versus a $0.75 incandescent saving $12/year on electricity, the net payback is about 3.5 months. After payback, every month is pure savings for the remaining 10+ year LED lifespan.
Does the number of bulbs I replace significantly affect total savings?+
Yes — savings scale linearly with the number of bulbs. Replacing 10 bulbs that each save $12/year saves $120/year total. Large households or commercial spaces with dozens of fittings can see hundreds of dollars in annual savings from a single LED retrofit.
How does hours of use per day affect the LED savings calculation?+
Energy cost is directly proportional to usage hours. A bulb used 8 hours/day generates nearly three times the savings compared to one used 3 hours/day. High-use fixtures — kitchens, living rooms, offices — benefit most from LED upgrades, while rarely-used closet lights offer smaller absolute savings.
Can the LED savings calculator be used for halogen and CFL bulbs too?+
Yes. Enter the wattage of your existing halogen or CFL in the “old bulb wattage” field and the wattage of the LED replacement in the LED field. A 42W halogen replaced by a 6W LED, or a 14W CFL replaced by a 9W LED, can both be modeled this way. The formula is identical regardless of the old bulb type.
Why might my actual savings differ from the calculator’s estimate?+
The calculator assumes a flat electricity rate, constant daily usage, and that the bulbs produce equivalent brightness. Real bills may include tiered rates, time-of-use pricing, or standing charges. Actual usage may vary seasonally. Also, incandescent waste heat can slightly reduce winter heating costs — a nuance the calculator does not model.
How do I calculate CO2 savings from switching to LED bulbs?+
Multiply the annual kWh saved by your grid’s emissions factor (kg CO2 per kWh). The US average is roughly 0.386 kg CO2/kWh (EPA data). If switching saves 93 kWh/year per bulb, that avoids about 35.9 kg CO2/year — roughly equivalent to driving 90 miles in a typical petrol car. Enter your local emissions factor for a country-specific estimate.
Does dimming an LED bulb save additional electricity?+
Yes. Most dimmable LEDs draw power proportional to the dimmer setting, so running at 50% brightness consumes roughly 50% of the rated wattage. For the most accurate calculation when you regularly dim your lights, use an average wattage (e.g., 5W instead of 9W) as your LED wattage input.
Disclaimer
Sources
Formula and data last reviewed by the TheCalculatorVault team on 26 June 2026. Figures are for general information, not professional advice.
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