Quick question about mortgage calculations!

[David L.]

I've been crunching numbers on various deals and I've been using mortgage calculators and they differ drastically! 

Zillow is showing for a $200,000 property with 5% down, $1241/mo. Zillow includes PMI and insurance is 800/year, property tax 1.2% with 3.5% interest.

Mortgagecalculator.org is showing $1098.09/mo. Same $200k, 3.5% interest, 1.2% property tax, .5 PMI.

Bankrate is showing $898.09, doesn't seem to include PMI.

Obviously this can make or break a cash flow deal because the difference is practically $300!

I am looking at zillow and zillow is always on the high side, bank rate being too low. 

The rents in the area are going for $1200-1400 for this property. If I go with bankrate, I would be cash flowing $300+. According to Zillow, I can range negative cash flow to $200.

What's the best way to calculate the margins? 

I can call the lender but that means I have to call every time or should I call a few times and compare between calculators to see which one is most accurate?