I can think of three reasons for that. One of them or any combination of them could result in such an illogical at first glance situation:
• You made an extra payment towards the principal some time ago and now it’s taking effect. The balance has become so low, that even a higher rate cannot push the actual sum of the monthly payment to its previous margin.
• The PMI got cancelled by the lender. Under the provision of the 1999 Federal law, lenders are required to cancel private mortgage insurance on most home mortgage loans made after July 29, 1999 automatically when amortization has reduced the loan balance to 78% of the value of the property at the time the loan was made. An earlier cancellation at 80% of the property’s value is likely to happen only if initiated by the borrower himself.
• If the rate has increased, but the amount of your monthly payment remained unchanged or went up insignificantly and then froze at that level, you may be in trouble, because these are the symptoms of a monthly payment cap in action. Check your mortgage contract: Is your mortgage an adjustable rate mortgage? Does it carry a payment cap? If this is the case, you should immediately look for ways to avoid negative amortization, and fast, before it increases the outstanding balance of your mortgage and wastes a lot of the effort you have put into paying the debt off.

Normally, your monthly payments do not include anything to be paid towards the principal during the interest-only period of your mortgage. On the one hand, it makes these payments lower; on the other hand, when the interest-only period is over you have to face the debt you borrowed years ago in its full size again, only now you have a shorter period of time to repay it. That is why it is strongly recommended to make voluntary extra payments towards the principal during the interest-only period, if your lender allows you to. If he does, make sure the outstanding balance gets adjusted immediately after an extra payment is made. Sometimes a special arrangement for extra payments during the interest-only period is included into the mortgage contract. If you are only planning to take out an interest-only mortgage and intend to make extra payments, pay special attention to these details in your contract. The problem is that many lenders do not adjust the balance during the interest-only period at all, with or without extra payments, unless stated explicitly otherwise in the contract. If the balance gets adjusted (becomes smaller), the amount paid as interest (percentage of the outstanding balance) becomes smaller, too. This way your monthly interest-only payments become even lower (provided the rate is unchanged or drops). If the first adjustment will take place only after the interest-only period is over, all the monthly payments during the interest-only period remain unaltered. It does not mean that you will eventually pay more as interest, though. Everything will be recalculated, your extra payments, as well as the overpaid interest, will be subtracted from the balance, when the time comes. The tricky part here lies in the investment opportunities available to you at the time of your extra payments. It may so happen that an alternative investment would have brought you a better return, if you had invested into it, rather than the mortgage, whose return you will see only in a few years.

For more on Interest-Only Mortgages read here.

A borrower has to pay Private Mortgage Insurance (PMI) only if he cannot make a 20% down payment. So, the ways to avoid the insurance are the ways to find enough cash to be able to pay at least 20% of the price of the property in question. Nowadays, the following options are available: a second mortgage; a “piggyback” mortgage; and lender-paid mortgage insurance.

If you already have a mortgage with PMI, you have to bear in mind that you have all the right to have PMI terminated as soon as the outstanding balance hits the 80% of the purchase (or recently appreciated) price of your property. “Recently appreciated” is your opportune key to freedom. If your property has appreciated in value, the absolute amount of 80% of its current price is higher. What’s your advantage? Say, you have a property that was $100.000 worth when you bought it. 80% of this amount is $80.000. This is the magic number that allows you to cancel PMI. You have been paying the mortgage off for some time and your current outstanding balance is $90.000. If your home has appreciated, say, $10.000 through these same years, its current value is $110.000. 80% of this amount is $88.000, which means that with your outstanding balance of $90.000 you are only $2.000 (not $10.000) away from canceling PMI. Neat, isn’t it? Terminating the insurance, however, is not an easy business. Read about the troubles and tribulations involved in my special article. Yet, just one more thing that I want to draw your attention to – the appreciated value of the house has to be documented by an appraiser, accepted by your lender. The procedure is not cheap, so you have to see first if the appraisal will really save you anything in the long run.

Another way to shorten your PMI period is good old extra payments towards the principal. If your mortgage carries no prepayment penalties (any more) each extra penny towards the principal will bring you closer to the 80% margin.