The sort of information which you could use to make an estimate of effective life of an asset includes:
- the physical life of the asset
- engineering information
- the manufacturer's specifications
- your own past experience with similar assets
- the past experience of other users of similar assets
- the level of repairs and maintenance commonly adopted by users of the asset
- retention periods
- scrapping or abandonment practices.
You work out the effective life of a depreciating asset from the asset's start time.