<prompt> Human: Ive read MMMs article on the math behind early retirement a few times, and it suddenly hit me that Im not really sure how to consider my mortgage on this.Ive also been planning lately to buy investment properties, which should grant me plenty of income once they are paid off. But in the meantime, it screws with the numbers, doesnt it? My spending, in terms of paying off mortgages, is temporary even if it takes several years. At retirement, those costs wont exist, or at the very least, the rent pays for the costs until theyre done.Do I consider the income I take from the investment properties, and put towards the mortgages as savings?Can someone help me decipher the math on this one?  <response>: Ive also been planning lately to buy investment properties, which should grant me plenty of income once they are paid off. Keep in mind, this only makes sense if they produce more cash flow appreciation than youd otherwise see in stocks. And in retirement, youre better off with something more diversified, so you wouldnt want to hold most of your net worth in RE.If youre going to be holding that mortgage for many years into retirement, its best to think of it as a living expense. You could also call the interest, taxes, and insurance a living expense and the principle payment savings. 