The calculators here compare fixed-rate and adjustable-rate mortgages in terms of the interest cost as a percent comparable to the interest rate.

The mortgage interest calculators are designed to help you choose between FRMs and ARMs. For background reading, I suggest Choosing Between Fixed and Adjustable Rate Mortgages, and Annual Percentage Rate (APR) Versus Interest Cost on a Mortgage. The question is the same one covered by Mortgage Comparison, the difference being in the methodology. The calculators here use interest cost analysis while the others use future value analysis. They are equally valid and should give the same answer 99% of the time.

Interest Cost Calculator: Fixed-Rate Mortgage Versus ARM With No Negative Amortization.
For borrowers trying to decide whether they should select an ARM without negative amortization or an FRM based on the lowest after-tax interest cost.  

Interest Cost Calculator: Fixed-Rate Mortgage Versus ARM With Negative Amortization.
For borrowers trying to decide whether they should select an ARM with negative amortization or an FRM based on the lowest after-tax interest cost. 

Interest Cost Calculator: Comparing Two Fixed-Rate Mortgages.
For borrowers trying to decide which of two FRMs they should select based on the lowest after-tax interest cost.