The thing with inventory write-offs is that it’s tempting to use straightforward math for determining the write-off amount.

Once something has been in stock for a year and it hasn’t been sold, doesn’t it feel like that it should automatically be written off like 50% or even fully? For some it seems and others it doesn’t. There’s nothing wrong with being more conservative, but little too much isn’t also all that good. 

Using straightforward math does make sense if your inventory includes too many items of small value for individual assessment. However, once there are items with higher value and fewer positions it always makes sense to assess them individually. Nobody said this was easy, it’s supposed to be time consuming if you don’t monitor your inventory levels and possibly slow moving positions regularly.

My word of advice is to use common sense above all and if it seems like too much work (and not just because you haven’t bothered to do anything about your positions before) then use math.