When adding an asset owned jointly with another person (or persons), you record the "at death" value from the deceased's estate point of view.
1. Joint Tenants
Where an asset is wholly "passed by survivorship" to the living joint owner(s) on the death of your deceased person, record 100% of the at death value in Probate Plus.
The asset is added to Probate Plus for information purposes and IHT form filling, but as far as the estate accounts are concerned, there is nothing further to be done and this asset will not appear on the assets report.
2. Tenants-in-common
Where an asset was held as "Joint tenants-in-common", the deceased's share of the asset is recorded as the "at-death" value. E.g. a ½ share in a £600,000 house would be recorded with a base value of £300,000.
You could set the asset description to something like “1/2 share of house at XYZ”, the holding as 1 and the base value as the value of the joint share. What you’re telling Probate Plus is that we have “one ½ share in the house valued at xxx”.
N.B. It is not advisable to put 0.5 in the 'Nominal' field and record the base value as £600,000 because if you run an Asset report it will describe that asset as 'Part retained'.