There is no significance to 22 percent with FHA home loans. This is where the 22 percent figure comes in:
If you have a conventional (non-government) mortgage with mortgage insurance, the insurance must automatically drop off once you have paid the loan down to 78 percent of the home's purchase price or appraised value. That is the value of the property when you took out the loan that you want to refinance -- the most recent loan on the property.
Mortgage insurance never goes away with today's FHA loans, and if you refinance from an FHA to a new FHA mortgage, you'll still pay mortgage insurance, even if you owe less than 80 percent of the property value.
The only way to cancel FHA mortgage insurance for recently-acquired loans is to pay them off by selling the home or refinancing to a conventional home loan. Just dropping the mortgage insurance could save you money, and if you could improve your rate as well, refinancing could be a smart move.
The refinance loan-to-value gets calculated using the property's current appraised value. If you bought your house for $100,000 and put 5 percent down, and a few years later refinanced its $85,000 balance, the lender would appraise the home. Suppose its value increased to $107,000? In that case, your loan-to-value would be $85k/$107k, or 79.4%, and you would pay not mortgage insurance.