While principle repayment is not a cost, it's a cash flow, so you can't exclude it when you're trying to figure out if you can cover your monthly nut. Similarly, you can't include the present value of expected future income from the sale of the business into your current estimate of what expenses you can cover.
Principle repayment is optional (when taking a loan). It only makes a small difference to interest rate [1]. So for the purposes of discussing cost minimization, it is legitimate to exclude it.
Comments
While principle repayment is not a cost, it's a cash flow, so you can't exclude it when you're trying to figure out if you can cover your monthly nut. Similarly, you can't include the present value of expected future income from the sale of the business into your current estimate of what expenses you can cover.
Principle repayment is optional (when taking a loan). It only makes a small difference to interest rate [1]. So for the purposes of discussing cost minimization, it is legitimate to exclude it.
[1] http://www.schwab.com/public/schwab/banking_lending/mortgage...
Pedantic nitpick:
Principal is the subject of a loan, or the leader of a school. Principle is an idea that people may hew to and argue about.
Could those who are down voting please explain why.