# Service charge apportionment calculator: what each flat pays and the works cost that triggers Section 20

> Enter the block budget, the reserve contribution and a flat's lease percentage to see its yearly charge, each demand, and the works cost that needs Section 20.

- Page to cite: https://aeolookup.com/block-management/service-charge-apportionment-calculator-per-flat/
- Publisher: AEO Lookup (https://aeolookup.com/)
- Section: Block and property managers, Service charges and arrears
- Published 1 October 2026
- Key fact: In a block with a £48,000 budget and a £6,000 reserve contribution, a flat with a 4.5% share pays £2,430 a year, £1,215 on each half-yearly demand. If 4.5% is the largest share in the block, works costing more than £5,555.56 take that leaseholder over £250 and need Section 20 consultation first.
- Sources: Landlord and Tenant Act 1985 section 20 and the Service Charges (Consultation Requirements) (England) Regulations 2003 (SI 2003/1987) for the £250 and £100 thresholds, read 2026-10-01; the arithmetic is our own, checked by hand. The test record is in tests/warden/tools-check.txt.

"How much will my flat pay?" and "Do we need to consult on this?" are the same sum run in two directions. Both start from the percentage in the lease.

**Free tool on the page:** Service charge apportionment calculator: what each flat pays, each demand, and the works cost that triggers Section 20. It runs in the browser at https://aeolookup.com/block-management/service-charge-apportionment-calculator-per-flat/#tool and asks for no sign-up.

## What the calculator does

It takes the budget for the block and the reserve fund contribution, multiplies each by the flat's share, and divides by the number of demands a year. Then it runs the sum backwards: at that share, what cost of works puts one leaseholder's contribution over £250?

With the figures it opens with:

| Item | Sum | Result |
|---|---|---|
| Service charge | £48,000 × 4.5% | £2,160 |
| Reserve fund | £6,000 × 4.5% | £270 |
| Flat's charge for the year | | £2,430 |
| Each half-yearly demand | £2,430 ÷ 2 | £1,215 |
| Equal split between 24 flats | £54,000 ÷ 24 | £2,250 |
| Change on last year's £44,000 budget | £4,000 × 4.5% | £180 more |

The equal-split line is there because leaseholders do that sum themselves. A flat on 4.5% in a block of 24 pays £180 a year more than one twenty-fourth, and the first email after the demands go out will ask why. The answer is that the lease sets the share, often by floor area or by a schedule fixed when the block was built, and the manager applies it; the manager does not choose it.

## The lease decides, not the calculator

Before you use any percentage, read it from the lease, not from last year's spreadsheet. Three things to look for:

- **More than one schedule.** Many leases split costs into parts: the building, the estate, the lift, the car park. A ground-floor flat may pay nothing towards the lift. Run the calculator once for each schedule with its own budget and add the results.
- **Shares that do not add up to 100%.** Where flats were added or leases varied, the percentages can total more or less than 100. That is a legal question for the client and their solicitor, not something to smooth over in the budget.
- **"A fair proportion".** Some leases give no figure and leave the share to the landlord or the surveyor. Record how the share was set and apply it the same way each year.

If the lease percentage is blank in the calculator, it uses equal shares, which is right only where the lease says so.

## The Section 20 figure

The law does not set a total cost at which consultation starts. It sets a figure per leaseholder: consultation is needed before qualifying works if any one leaseholder would have to contribute more than £250. So the works cost that triggers it depends on the largest share in the block.

At a largest share of 4.5%, £250 ÷ 0.045 is £5,555.56. A roof repair quoted at £5,400 including VAT is under it; one at £5,800 is over, and without consultation or dispensation each leaseholder's contribution is capped at £250. In a block where the largest share is 10%, the same threshold is £2,500.

For a contract lasting more than 12 months, the test is £100 a year for any one leaseholder. At 4.5% that is a contract costing more than £2,222.22 a year. A lift maintenance or cleaning contract can cross it.

Always enter the largest share in the block for this part, not the average. Our [Section 20 checker](https://aeolookup.com/block-management/section-20-consultation-threshold-and-timetable-checker/) works out the dates once you know consultation is needed.

## Before the demands go out

The amount is half of a valid demand. The other half is what the demand carries with it: the landlord's name and address, the summary of rights and obligations, and the timing against the 18-month rule. Our [demand checker](https://aeolookup.com/block-management/service-charge-demand-validity-checker/) tests those, and the [service charge year calendar](https://aeolookup.com/block-management/service-charge-accounts-when-due-calendar/) sets the dates for the year.

Two habits save the most correspondence. Send the budget with a one-line reason for each heading that moved by more than a few percent; the 9.1% rise in the example needs a sentence saying which headings moved. And state each flat's percentage on the demand, so the leaseholder can check the sum without asking.

## Limits

This is arithmetic on the figures you enter. It does not read your lease, and it does not tell you whether a cost is recoverable or reasonable; those are questions of law and of the lease. England only: the thresholds quoted are from the English regulations.

Overlyft ![](https://aeolookup.com/img/d/ours-badge.png) can set up an AI assistant that runs the Section 20 test on the largest lease share and drafts the notices for a property manager to check. The percentages still come from the lease, and a person still signs the demand.

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General information for UK small firms, not legal, tax or financial advice.