For commercial REI, is assessed value = purchase price?

[Ryan Johnson]

We are building a spreadsheet that allows us to plug in a few numbers and obtain a quick result.  I am trying to determine if it is better to simply use the purchase price multiplied by millage rate or if I should utilize last year's property tax rate.  Is the assessed value for the first year (thus determining property taxes) equal to the purchase price (say for an apartment complex) or will it be evaluated each individual time?   Thanks for the help!