The business should have grown at a 5% rate too to compensate deflation. The interest paid monthly could be nominally constant in this case. Only the very best investments will get funded with deflation.
All other things being equal, the benefit of investing over hoarding should be currency-neutral. That is, if an inflationary currency would lose 3% due to inflation if hoarded but gains 2% due to interest, a deflationary currency should also perform roughly 5% better if loaned rather than held.
I'm assuming 5% nominal interest for both cases in my example.
There are two fallacies that lead people to the opposite conclusion:
1) Thinking that a deflationary currency is extra valuable to hold and forgetting that this means it has greater spending value too because the person you spend it with gets to hold it if they want. The value of the deflation comes from the lender and is carried through the transaction to the end.
In my example, the baker spends the money to buy real capital, he doesn't hold the money.
2) Forgetting that the cost of inflation comes from the expansion of the money supply. This expansion acts as a tax on all wealth since the newly-printed money can claim any wealth in the economy. The cost of the inflation acts as a claim against the lender's wealth and is also carried through the transaction to the end.
Yes, monetary inflation acts like a tax over any wealth and (if unexpected) damages in a special way to lenders.
If expected, it is just added to the nominal interest to maintain the real interest.
The benefit to the borrower is from being able to consume earlier than he could otherwise. This value is currency-neutral and it is this surplus that is split between the lender and the borrower.
But with deflation, money has an advantage over other capitals. When you buy capital, you expect its yield to be at least as good as basic interest (real interest less risk premium), thus the price of given capital can be calculated at any time from the basic interest rate in the market and the revenue you obtain with that capital. Deflation decreases the revenue, devalues real capital and therefore discourages its accumulation.
With deflation more than ever, money becomes the better of the capitals.
Do you see something wrong with my example?