Should I use land value allocation at the time of purchase or sale?

Hi,

When trying to allocate the sales price for rental properties, I have trouble finding the good reference about how to allocate the sales price of land vs improvement? Should I use the improvement/land breakdown from the tax assessor when I purchase the property or on the year sale?

 

For example:

When I purchase the property in 2010, the tax assessor has the following allocation:

Improvement: $75,000

Land: $25,000 (25% of total value)

 

When I sell the property in 2021, the tax assessor shows the following allocation:

Improvement: $140,000

Land: $6,000 (30% of total value)

House is sold for $250,000

 

How should I allocate the sales price of $250,000, should I use 25% as the land value (the allocation in 2010) or the 30% as the land value (allocation in 2021)?

 

Thank you!