Splitting Duplex into Separate TMS Numbers

[Andrew Merritt]

I recently purchased a duplex and one of the tenants approached me, interested in buying his unit outright.  This is generally not something I'm interested in doing, but it's worth looking into.  It should be doable, I've seen other duplexes in the area that have two separate TMS numbers.  What I'm curious about is what kind of premium is usually paid for the unit.  Obviously, a 50% of the purchase price would not be worth it for me, but 70% might.  Is there a common ratio that's used to estimate the split, or just use single-family comps from around the area?