In the New Build Boost mortgage scheme, your equity loan is a loan tied to the value of your home.

The 15% boost is an equity loan which is frozen for 5 years.

This means the value of the boost starts out with a value equal to 15% of the purchase price of your property.

After 5 years, if there’s any remaining boost balance, its value will “step up” to reflect any change in the value of your property over the last 5 years, and will keep tracking up or down with the value of your home until you pay it off completely.

This means you could pay off more or less than you originally borrowed if you pay the boost back after 5 years.