In addition to the down payment, you'll also have to pay closing costs — miscellaneous fees charged by those involved with the home sale (such as your lender for processing the loan, the title company for handling the paperwork, a land surveyor, local government offices for recording the deed, etc.).  The average closing costs percentage is usually about 2-5% of the purchase price (e.g., ~$4500 on a $180,000 home), but 1-8% is not uncommon.  And to be clear, nobody chooses a specific percentage number—the closing costs will just happen to add up to some percentage.

Your lender will give you an estimate of closing costs on the purchase of a particular house you've selected. This is called a "Good Faith Estimate" ("GFE"). If they don't give it to you, ask for it.

Here are typical closing costs, along with a calculator to help estimate the cost for your own home.  Everyone's situation is different, and this calculator is not a substitute for getting the GFE from your lender.  When you actually close, the closing costs will be detailed on the Settlement Statement.  As you get close to closing, ask the Title company for a copy of the statement so you can review it prior to closing for any surprise charges.