How do you choose useful life for a PP&E step-up, and what is the trick with useful life extension?

Useful life should reflect the remaining economic life of the acquired asset, not the target's old depreciation schedule. Appraisers assess asset condition, replacement cycle, maintenance history, and expected use. The trick is that fair value step-up can come with a longer remaining useful life than book accounting implied, so incremental depreciation may be lower than a simple step-up divided by old life would suggest.