It varies by situation, but a couple decent benchmarks are if it improves your rate by 1% or more, or you recover the refi costs in two years or less.

I have helped a lot of rookie investors get their first property over the years. 

I bought a 4 plex a year ago and I live in one unit while saving for another.

According to google, it should last at least 50 years. 

Even though I am a Broker I dont sell real estate ( that I dont own ) for many years now..

Can they be 30 years, or is 10-15 years more typical?

My Start in Real Estate46 years ago I decided to switch “careers” and left international banking and became a licensed real estate broker.

.- 10% Pop Growth over the past 10 Years- 10% Job Growth over the past 10 Years- Low Crime- High Appreciation- Manageable Entry Prices- At least 30% Renter PopulationHere's an example of all those rules of thumb with a crime map of Austin, TX.

If you want a lower tax bill then you would want deductions immediately, if you want profitability in the short term then you would want to depreciate as that spreads depreciation expense over the years.

For example, say the owner took out a 1 Million loan for his building 5 years ago, now is selling it at 2M.