Estimate rough yearly savings and simple payback from swapping older bulbs to LED, based on wattage, runtime, tariff and total replacement spend.
Last reviewed: 16 April 2026 - UK-focused estimate, not a product review
LED swaps are usually strongest where older bulbs still run for long stretches every evening. The financial case is much weaker in spare rooms, lofts and other spaces used only occasionally.
This works best when you compare the fittings you actually use most, not every bulb in the house treated as if it had the same hours.
Kitchen, living room, hallway and outside lights often give a much stronger answer than occasional-use fittings.
Six older 50W bulbs used most evenings often give a much stronger payback case than a larger number of low-use bulbs scattered around the house.
The saving is still real, but low-use rooms rarely change the annual bill enough to feel urgent unless the bulbs are very power-hungry.
The wattage gap, the daily hours of use and the total cost of the swap matter far more than brand differences between one LED bulb and another.
Treat this as a prioritising tool rather than a reason to swap every bulb in one go.
Another lower-cost route worth comparing when you want easier wins first.
Compare a quick lighting payback against a larger fabric-upgrade decision.
Another calculator-led savings decision where replacement cost changes the case.
Review why this calculator is strongest when runtime is clear and fittings are used regularly.
They can, especially in rooms where lights are on for hours most evenings. The savings are much weaker in low-use rooms.
The big drivers are the wattage gap between the old bulb and the LED, the daily hours of use, and the total replacement cost.
Not necessarily. The strongest financial case is usually the highest-use rooms first, then occasional-use spaces later.