If I read this right, you want to have access to the money in 4-5 years in order to put the money into your mortgage.
If you just put it into your mortgage immediately, you are guaranteed a tax-free return of 5.1%. I doubt that you will be able to find another guaranteed after tax return anywhere near that.
Yes, you may be able to get a higher return with other investments. But in a five year time frame, many investments will have a lower return and possibly even a loss. Is it really worth the risk if you are going to put it into your mortgage in five years anyway?
|