A Berlin rent rise has to clear four separate hurdles, and only one of them is the famous 15 per cent. Put in your own figures and dates and the tool shows which hurdle stops the letter first, and the two dates you are actually working to.
The Mietspiegel value is the one for your own building, not a city average. Look it up by street at the Senate's Mietspiegel query service. The 7.71 shown here is only the citywide median of the 2026 edition, so treat it as a placeholder until you have replaced it.
Nothing added yet, so the tool assumes the rent you pay now is also what you paid three years ago.
Modernisation and operating cost rises are the ones that trip people up. They are real money out of your account, but section 558(3) BGB leaves them out of the 15 per cent, so adding them here raises your ceiling rather than lowering it.
Checked on 13 September 2026 against sections 557a, 557b, 558, 558a, 558b and 559 BGB and the Berlin Kappungsgrenzenverordnung of 14 March 2023. This is a reading aid, not legal advice, and it cannot see your contract. If the numbers look wrong to you, take the letter to a Mieterverein or a district Mieterberatung before the reply date passes.