A mortgage in principle usually lasts between 60 to 90 days. However, it is not the end of the world if it runs out before you submit your full mortgage application. If it does happen to expire before you come round to getting your full mortgage, you can always re-apply for another. One bit of advice we would give however would be to not get more than two MIPs in an 8 month period. This is because every time you request one, a credit search is applied. If you do this too many times it could start to badly affect your credit score.