All good answers and advice given to you already. The "average" really doesn't tell you much. In the last 3 months a TOTAL of 310 units (ranging from $600-$5500 with an avg of $1914) have been rented in Naperville as reported in the MLS and the "average" time it took to rent was 27 days. This can be broken down further to look at specific areas, price ranges or townhomes only, etc., but you get the point. The additional advice that I would offer is to seek out a very good mortgage broker or talk to several to get good advice and info before you proceed. I don't want to make any assumptions here because you may owe nothing on your townhome and be purchasing your new home with cash, but if that is not the case, your purchase lender will look closely at what you will do with your existing townhome and will not use any rental income towards your loan qualification. The general guideline today is that you need to show rental income for 2 years on your tax returns before it can be used. You may have no trouble at all, and I hope that is the case, but if you would like a referral for a good broker (she was the Pres of the IL Assoc of Mortg Professionals 2 yrs ago) please contact me. Best of luck! You are going to be in a good position in both transactions......strong rental market and great buyer's market!