Your expense is that you've hitched yourself to an oversized loan, so you're putting money from one pocket to another, except the latter has a hole in it and yo

Your expense is that you've hitched yourself to an oversized loan, so you're putting money from one pocket to another, except the latter has a hole in it and you have an obligation to keep feeding it. If your cost was only mortgage interest, you'd be happier with 600k outstanding at 1% than 300k at 4% for the same house.