When you may adjust the advance payment
Under section 560 (4) BGB, either party may adjust the advance payments to a reasonable amount after a statement. This is done unilaterally by a declaration in text form; no consent is needed. It works both ways: the tenant may also reduce an advance that is too high.
This means the allocable operating costs under section 2 BetrKV, including heating costs. The heating cost advance is an advance on operating costs (section 556 (2) BGB) and therefore belongs in the comparison.
A flat-rate service charge has no statement. It falls under section 560 (1) to (3) BGB, and the calculator gives no result for it.
How to calculate the new advance
The basis is the tenant's cost share from the last statement. If they lived there all year, you divide it by twelve. Only cost changes that have already happened or are concretely expected are added, as a euro amount with a reason.
The comparison uses the agreed advance, not the amount actually paid. A balance due that arises only because the tenant did not pay is no reason for an increase.
New monthly advance = (cost share per statement + concrete foreseeable changes) ÷ 12
Worked example with an announced gas price increase
- Cost share per 2025 statement: €2,640.00, of which €1,200.00 heating costs
- Current advance: €180.00 per month, i.e. €2,160.00 per year. Balance due: €480.00
- The gas supplier announces a 20 % increase: 20 % of €1,200.00 = €240.00 per year
- New advance: (€2,640.00 + €240.00) ÷ 12 = €240.00 per month
A flat surcharge of 10 % on everything would give €242.00. That would not be permitted (BGH, VIII ZR 294/10).
Move-in during the year
If the tenant moved in during the year, divide the non-heating costs by their months of use. Project the heating costs to a full year using degree days, not time. Someone moving in in May has not paid for the expensive winter months of January to April.
Example: move-in on 1 May 2025, non-heating costs €1,000.00, heating costs €300.00. Non-heating: €1,000.00 ÷ 8 = €125.00 per month. May to December equal 470 ‰ of the degree days, so heating for a full year is €300.00 ÷ 0.47 = €638.30 or €53.19 per month. Together €178.19, rounded up €179.00. Split purely by time it would only be €162.50.
Hot water is used fairly evenly all year. CIRO therefore projects it by time and only space heating by degree days. With less than three months of use or less than 150 ‰ of the degree days, the calculator gives no amount because the projection is not reliable.
From when the new advance applies
Section 560 (4) BGB does not name a date. According to a widely held view, the adjustment takes effect from the next due date after the notice is received. A stricter view applies section 560 (2) BGB by analogy: then from the start of the month after next following receipt.
The calculator shows the later date as "safely applies from". If your notice is received on 20 October 2026, that is 1 December 2026. At worst you give away one month.
Common mistakes
- Adding a flat 10 % buffer: there is no room for that (BGH, VIII ZR 294/10).
- Adjusting without a correct statement: the adjustment requires a statement that is correct in form and content (BGH, VIII ZR 246/11).
- Forgetting the heating cost advance: operating and heating cost advances belong together in the comparison.
- Rounding up to €5 or €10: that is a hidden surcharge. Rounding up to whole euros is common and justifiable.
- Projecting from a short tenancy: under six months the projection is unreliable.