Negative p.a. rate for a 12-month loan

Banks do all kinds of crazy things to attract customers. Paying 4 euros seems like a very low price for customer acquisition. So really the thought is that you would get this loan from them and be their customer for life.

For some people, there are a lot of better ways to earn 4 euros. The hassle of having to make a monthly payment may not be worth it.

I would be tempted to take this offer. Borrow the money, use it to earn more money, and set up an auto draft. And that is really the power of this offer; I am a person that does not borrow money. By giving me a small amount of money, I am tempted to become a customer.

When you consider banks here in the US will give customers hundreds of dollars to open a checking account, this seems like a small price to pay even when one factors in defaults on the loans.

As Pete B. said, it's most likely customer acquisition. However, I'd be wary of two things:

• Any hidden costs, e.g. a monthly fee for your monthly payment, variable interest rate, any add-ons like a permanent bank account with that bank (with a monthly fee), etc. With these costs the bank might the winning party here.
• Advertisement agreements, e.g. agreeing to be contacted via phone, mail, or email.

Also, stocks are not necessarily the best investment option for a 12 month period. What if there's a huge, 2nd virus wave over Christmas? Personally I think there's too much volatility within one year. Better options might be short term bonds or discount certificates.

I think you are making it overly complicated with "long term employed" and "market recovery within the next 10+ years". There is no need to invest the borrowed money in stocks. Just keep it in a savings/checking account (those presumably don't pay significant interest, but don't cost interest either). Make the monthly payments out of the account and you will have an extra €4 left at the end. That is sufficient to show this is a good deal (assuming there are no hidden fees). Any additional investment strategy is optional.

Incidentally: "market to fall more than 0.4% within the next year which is an obvious bet" -- this is wrong (and irrelevant) -- stocks are a risky investment and their expected return is not the same as the risk-free interest rate. See here.

Since 18 September last year, the European Central Bank has paid -0.5% on overnight deposits from Eurozone banks. If the bank is charging you -0.4% interest, they’re still doing better than they would be if they weren’t lending the money out.

Don't forget this is a credit just like any other. It will affect your credit rating. This will be good if everything happens just as planned, but bad if problems occur. The credit will show up until paid back, so if you need another credit until then, you might get problems, as you already have one.

Lastly, your rights as a customer may be reduced, e.g. regarding premature canceling. I could find hints about 0% credits only and seems to have become better in the last years, but negative payments are so new no court had to rule about them yet.

Some thoughts on this

1. Are you actually going to get it? You probably only get it with a perfect credit rating in which case you are unlikely to actually need it and spend some of your time to earn 4€. This is probably rather meant as an advertisment to get people with a lesser credit rating interested and selling them something that will have positive interest
2. A bet on a stock market recovery...the German stock market is almost at it's all-time high. There is not much to recover any more. In many other countries markets are also a lot closer to what they were one year ago than one might expect in the middle of a pandemic. Nobody knows the future but I do not see much of a recovery coming up. Volatile investments for a short fixed time frame are also problematic. And for the non-volatile investments you are almost not getting anything
3. Interest in general is very low at the moment. If you finance real estate you can easily get 0.5-0.6% interest for 10 years.
4. If you are a bank and park money at the central bank you are paying dearly and it does not look like this is going to change anytime soon