There is no way to give a true answer without knowing all of the details of your transaction. It sounds like you want to refinance. If you only have 4 years remaining, then most of your payment right now is NOT interest. So, refinancing may hurt you more than help.
Remember that locking in your mortgage may carry additional fees or penalties, all designed to swing the balance of probabilities over in favor of the bank. The bank has already set the variable rate and the down payment so that they expect to profit (in general) from the mortgage, so the only way that you can really benefit from this situation is if the locking decision will cost you nothing, and the interest rate (on the mortgage itself) has dropped appreciably since you took it out. Certainly, if the current mortgage rate has dropped below what the *prime rate* was at the time you took it out, then time has been really good to you -- you may actually be making money compared to the bank, which may not.If you're confident that interest rates will remain low for the next few years, or if locking the mortgage rate in will cost you more money than you would expect to save with a modest rise in rates, you can let the mortgage rate vary.On the other hand, if you fix the rate of your mortgage, you can budget for exactly what the mortgage will cost you and be in a better position (information-wise) to make future financial decisions. Personally, I would do a mathematical analysis (or have an accountant do one for you) and determine what the costs would be of fixing the rate or letting it vary, and what the consequences would be if the interest rate went up by 1 basis point, 2, 3, etc. along with the odds of it doing those things in the next four years.My gut tells me, what with my penchant for certainty in life, to lock the rate in unless you have stiff penalties against that. But I'd run it by a financial consultant (not from your bank but a different one, possibly independent) for the final word.
-------------------------------------------------- Canadian housing and mortgage corporation