Is the 1% SWR accurate? Is there a reason to think that I can count on 1%, 4%, or another percentage in the future?
Yes and no. Yes, the 1% SWR conclusion is accurate. But no, I would not count on it being as low as 1% in the future.
The thing about SWRs is that they do not attempt to predict the future at all. They measure the worst retirement timeframes for a given country. The study you are looking at uses stock and bond data since 1900, and that timeframe covers two world wars that Germany lost. Nothing in that timeframe for the US economy that the 4% rule was derived from can come even close to the hyperinflation in the Weimar Republic where 1 USD was worth 4
trillion German marks in 1923. Can you imagine retiring in that situation? Me neither. I'm honestly impressed that a 1% SWR held up.
So the numbers are what they are, but I also don't expect that worst case situation to repeat in Germany any time soon so I wouldn't hang my hat on a 1% SWR. However, I wouldn't automatically assume a 4% SWR either. They're a lot more complicated than people think, especially once you start accounting for international data sets, diverse stock options (beyond a total market fund), exchange rates, and local inflation. For example, because of local inflation and exchange rates a US retiree and a German retiree investing in the
exact same US stock and bond funds will experience very different SWRs!
Definitely check out the article that Neonlight references above, and take the time to play with the
Withdrawal Rates calculator that has a setting for Germany. In that setting, "total domestic market" is German stocks, bonds are German bunds, and it also accounts for German inflation and exchange rates. All data is since 1970, which is long enough to cover lots of economic conditions while bypassing the WWII fallout. And you can also add international stocks to the mix if you like rather than focusing exclusively on the German market.