With today's technology, anyone can find a mortgage calculator online as well as find the average 30-year fixed rate. This is a great way to get a large ballpark estimate. However, the issues with that are there are many variables that are considered when determining someone’s rate and monthly payment. The other issue is that the posted average 30-year fixed rate is always a week or two behind and isn't accurate to where today's rate is.
One final issue with the online mortgage calculators that I find to be major, is that they don't give you what other funds for closing that you need to consider besides a down payment. In a typical mortgage transaction, you have lender and attorney fees, prepaid interest, escrow account funding, and government fees which can add up to a significant amount.
I realize how important this is for my clients to know so I have an online mortgage calculator that I can customize specifically for them to give them an accurate estimate of what their monthly payment would be on a specific property. I have also developed a spreadsheet that I customize to give them an estimate of their monthly payment along with funds needed to purchase a property and different purchase prices. This leaves no surprises for my clients and they can confidently search for a new home knowing what the payment can be and how much funds may be needed to purchase it.