But how can you ignore the interest? If the interest drops to along with your salary, you won't have to pay the same nominal amount each year - which is exactly what's been happening in the EU.
With deflation, interest rates might be low [0], but they aren't likely to decline over time (unless the rate of deflation is increasing), whereas salaries will decline over time. So the interest rate won't drop along with your salary. Your salary will drop, and while the interest rate might (with the caveat noted previously) be low, its not likely to go down over time (if it does do so constantly due directly to deflation, that means your salary is likely not only declining, but doing so at an accelerating rate), your salary will be dropping both in nominal terms and proportional to the interest payments on your debt.
[0] but probably not; availability of credit will be low because risk-free instruments -- cash -- with a positive expected real rate of return exist, so there is little incentive to lend. Low credit availability doesn't make low interest particularly likely (it does make high interest rate volatility more likely, though.)
For the calculations I ignored it. The discussion was inflation/deflation. Putting it in only changes my example by adding more arithmetic (calculating interest paid per period), but doesn't offer any insight into paying debts under inflation or deflation. EDIT: For the sake of this discussion pretend that the $100k paid includes the interest if you really want it to be there.
So in the EU interest rates are pegged to salary? Can it go negative? Because that's what needs to happen for loans under deflation to make sense. Your effective interest rate in a deflationary economy is deflation rate + interest rate. If you take out a 2% loan with 2% deflation your effectively paying 4% rates. The higher the deflation, the worse your rates become.
Now, if interest can go negative, then borrowing under deflation makes sense. But lending doesn't. Because the lender would be handing over money that would be more valuable kept under a mattress than loaned out at a negative interest rate.
Your loans would become more expensive, certainly. It's still not correct to say that the "mortgage payments are not going to go down", which is what I replied to. They would - to a certain point, at least.
With deflation, interest rates might be low [0], but they aren't likely to decline over time (unless the rate of deflation is increasing), whereas salaries will decline over time. So the interest rate won't drop along with your salary. Your salary will drop, and while the interest rate might (with the caveat noted previously) be low, its not likely to go down over time (if it does do so constantly due directly to deflation, that means your salary is likely not only declining, but doing so at an accelerating rate), your salary will be dropping both in nominal terms and proportional to the interest payments on your debt.
[0] but probably not; availability of credit will be low because risk-free instruments -- cash -- with a positive expected real rate of return exist, so there is little incentive to lend. Low credit availability doesn't make low interest particularly likely (it does make high interest rate volatility more likely, though.)