CGT for a widow on a previously co-owned property

My mother is a widow and has recently sold a small rental property which had been left to my late father on the death of his mother. When his mother died in 1999 my father was left the small property. In May 2005 joint ownership with my mother/father was established. In Oct 2017 my father died and in November my mother gained probate and full ownership of the property. This rental property was then sold March 2025. Does she pay CGT on 50% market value from date of probate (Nov 2017), or from May 2005 when joint ownership? Does she pay CGT at 50% or 100% market value from her husband's death until property sold, deducting CGT allowance of £3000 and selling costs? Does she need to take pre-2005 into any consideration?

Not HMRC...base cost is 50% of probate value in 1999 on gift from souse (spousal transfers take original acquisition values/costs) and 50% of the probate value in Oct 2017 when inherited the other 50%, value at May 2005 is not relevant (spousal transfers are not CGT events). CGT is payable on difference from those figures to March 2025 (less costs and exemption)....so you add 50% of the 1999 value to 50% of the 2017 value thats the cost, deduct that from net proceeds of sale and then the annual exemption and thats the amount liable to CGT

Hi Chris,
The purchase price is made up from her 50% share of the value in 2005 and then 50% of the value in 2017.
These are added together and the gain is then based on the increase from that figure.
She can then deduct the selling costs to work out the taxable gain and then claim the £3000 allowance.
Thank you.

HMRC...this is wrong...the property was inherited in 1999 and the mother owned 50% of the property from when gifted to her by husband in 2005, the spouse ALWAYS takes the spouses acquisition cost on gift it is NEVER revalued on gift between spouses...please correct this now!

HMRC...on spousal gifts the receiver ALWAYS takes the relevant base cost from the other spouse, that is a HARD AND FAST rule for CGT...its why spousal transfers (in this case 2005) are exempt. So, the 2005 value does not come in to this at all...its the 1999 value for the 2005 gift and the 2017 value for the other 50%. HMRC needs to correct its statement that its 50% of the value in 2005, it isnt, nothing happened in 2005 for CGT purposes, it was a spousal gift (exempt)...its 50% from 1999 and 50% from 2017. Look up the legislation on spousal gifts and base costs that the other spouse then takes!