Remaining useful life
Also known as RUL, Remaining lifetime and Remaining service life
Expected duration or number of uses a product can still provide before it becomes unusable.
The remaining useful life, is the estimated time or number of uses a product has left until it becomes unusable.
The remaining useful life can be expressed as:
- A duration: “100h of use left”
- A number of uses: “12 wears left”
- A percentage of use: “42% used”
- A percentage of remaining useful life: “58% of life remaining”
- A fraction of remaining useful life: “0.58 of life remaining”
Using a percentage or a fraction of remaining useful life is the preferred choice when doing carbon accounting. Since it’s a relative value, it doesn’t require to estimate the total useful life of the item.
The remaining useful life is used in avoided emissions to calculate the displaced emissions part of the formula. Items with a higher remaining useful life increase the avoided emissions because it will take longer to replace them.
WRAP
WRAP calls it "remaining service life" and treats it as how long a preowned item will keep being used, using the item's condition grade as a stand-in to decide which items qualify for Preloved Certified.
WBCSD
WBCSD calls it "remaining lifetime" and treats it as how long an existing piece of equipment would have kept running before its expected end of life, which matters when calculating avoided emissions for a solution that replaces it early.
Other standards
WRI, the GHG Protocol and ISO 14040/44 don’t define or use remaining useful life.
Aito
In the context of avoided emissions at Aito, the remaining useful life is calculated based on the condition of the item. Each condition is given a value:
- Brand new: 1
- Like new: 0.75
- Good: 0.5
- Fair: 0.25
- Damaged: 0.0
Then, an average condition value can be calculated for each product category, weighted by the number of items sold in each condition, giving a fraction between 0 and 1.
This fraction can then be used as a part of the displaced emissions formula.
Cite this entry
Aito. (2026). Remaining useful life. In Aito Knowledge Hub. Retrieved October 18, 2026, from https://aito.science/knowledge-hub/remaining-useful-life