Which Limit Actually Stops Your Berlin Rent Increase
A Berlin rent letter has to clear four separate hurdles and only one of them is the famous 15 per cent. Put in what you pay, what the letter asks, your own Mietspiegel value and the dates, and the tool draws the last three years of your rent against both legal ceilings so you can see which one the letter runs into.
The rules come from sections 557a, 557b, 558, 558a, 558b and 559 of the Buergerliches Gesetzbuch and from the Berlin Kappungsgrenzenverordnung of 14 March 2023, which cuts the national 20 per cent ceiling to 15 across the whole city. The default Mietspiegel value shown is the citywide median of the Berliner Mietspiegel 2026, published 28 May 2026, at 7.71 euro per square metre of net cold rent. Replace it with the field for your own street from the Senate query service, because the Wohnlage is assigned street by street and it is the most disputed line in these letters. Checked on 13 September 2026. This is a reading aid, not legal advice.
Start with the contract type, because a Staffelmiete or an Indexmiete blocks most of what these letters ask for. Then add any rises you have already had in the last three years, separating a comparable rent rise from a modernisation or operating cost one: only the first kind uses up your 15 per cent. The chart draws your rent history against both ceilings and marks what the letter asks, and the panel underneath gives you the date you have to answer by.
Two ceilings, and the lower one wins
A rise to the ortsuebliche Vergleichsmiete runs into whichever is lower: your current rent plus 15 per cent, or your flat size times your Mietspiegel value. Set those equal and the percentage only binds while you pay less than about 87 per cent of that value, which at the 2026 citywide median of 7.71 euro per square metre is 6.70. Above that line the Mietspiegel is your real ceiling and the 15 per cent never comes into play.
Modernisation rises push your ceiling up, not down
Section 558(3) BGB leaves increases under sections 559 and 560 out of the three year calculation, so a modernisation rise or an operating cost adjustment does not spend your 15 per cent. Entering one here raises what the landlord may reach in total, which is counterintuitive and is where most people get their own sum wrong. Modernisation has its own limits instead: 8 per cent of the chargeable cost a year, capped at 3 euro per square metre over six years, or 2 euro if the rent was under 7.
The two dates that matter more than the amount
Section 558b BGB runs on calendar months. You have until the end of the second calendar month after the letter reaches you to agree, and the higher rent starts at the beginning of the third. Silence is not agreement, but it opens the landlord three further months to sue for your consent, which is why partial agreement in writing usually beats saying nothing.
The clocks, and the form
The rent has to have been unchanged for 15 months on the day the rise starts, and the demand cannot be made until 12 months after the last rise. Separately, under section 558a(3) BGB the landlord has to quote the qualified Berlin Mietspiegel figures for your flat even when the stated reason is three comparable flats or a surveyor report, and a new managing agent who signs without attaching authority can be rejected straight away under section 174 BGB.