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.