Tax Assessed Value as Benchmark
No, I don’t have any hard data backing me up (and don’t have the time to compile it), but at least anecdotally, it sure seems that there’s a correlation between year built/last sale, and fair market value.
Here it is:
The newer the construction date/last sale, the higher the percentage; the older/less recent, the lower.
Put another way: the reliability of tax assessed value fades the older a home is and/or if it hasn’t sold in awhile.
So, for example, a 2009 townhome with a tax assessed value of $200k is likely worth pretty close to that.
By contrast, a 1975 townhome occupied by the original owner, with the same tax assessed value, probably has a fair market value quite a bit lower — as much as 20% less, or $160k.
Updates (or lack thereof); nearby competition (or lack thereof); location, etc. all affect — but don’t alter — the basic relationship.