How reliable are Mortgage Calculators online?

I like this one: Calculator

Even if they are accurate they may not include PMI (if you're not putting 20% down or have 20% equity), Homeowners Insurance and Property taxes.

Math is math. Put in the correct information and you'll get correct information out.

Just be aware of whether or not the final calculation includes property tax, insurance, etc

Monthly Payments :

Mortgage-Principle and Interest
Real Estate Property Taxes
Insurance

The online calculators are spot on calculating your mortgage, but you must add taxes and insurance for monthly payment total.

A calculator is accurate. Your inputs are going to be the issue. Knowing what the property tax rate and valuation is, knowing the insurance premiums, and nailing the final sale price and closing costs is what makes it vary. I always oadded that stuff. Mortgage has come in lower than estimated due to my conservative nature both times ive purchased. Just find the higher end of the range for everything and use that just in case.

Depending on where you live, your Tax Assessor's website may have a property tax calculator as well.

As accurate as the information you enter into them

Something else that can bite you.. those calculators use the property tax number based on what the current owner is paying. The current owner could be getting significant discounts based on senior citizen discount, disability, military service, etc....

My initial calculation was only $900/yr for property taxes, owner was senior citizen. My property taxes on the house are $3200.

When calculating your property tax estimate, look at a couple of the houses around it to make sure their taxes are all looking similar, before going with that number.