Hotel Room Block & Attrition Calculator: Block Size, Pickup Floor and Penalty

How it works

Peak rooms = attendees × % needing rooms ÷ (1 + % doubles) × (1 − % booking outside) · Room nights = peak × (1 + shoulder nights × shoulder %) · Suggested block = ⌈room nights × 90%⌉ · Pickup floor = block × (1 − attrition allowance) · Penalty = max(0, floor − pickup − resold) × rate × damages % · Comp nights = ⌊room nights ÷ comp ratio⌋

A room block reserves hotel rooms at a group rate. In return, the contract’s attrition clause makes the group pay for rooms it fails to fill beyond an allowance, so blocking too many rooms is expensive. With a 20% allowance, the group must pick up at least 80% of the contracted room nights; every room night below that floor is charged, usually at the group rate. The calculator sizes the block from the attendees who need beds, divided by the rooms shared by two people, minus the share who book elsewhere (short-term rentals, loyalty points, cheaper hotels). Arrival and departure nights are lighter than the peak night, so they count at the shoulder percentage. Contracting about 90% of that forecast leaves a cushion: if pickup is strong you can usually add rooms, but you cannot shrink a signed block without paying. To check an existing contract, enter the contracted room nights and the pickup so far. The calculator shows the floor, the room nights still to fill and the penalty if pickup stays where it is. Under More options you can credit rooms the hotel resold and set damages below the full rate, which some contracts allow because an unsold room costs the hotel less than a sold one. Attrition clauses are a form of liquidated damages: the amount is agreed in advance, so the contract’s wording decides how cumulative or nightly pickup, resale credit and outside-block bookings are counted.

Worked example

For 400 attendees with 60% needing rooms and 20% of rooms shared, 240 people need 240 ÷ 1.2 = 200 rooms on the peak night, and 150 of them are in the block after 25% book elsewhere. Over three nights with shoulder nights at 60%, that is 150 × (1 + 2 × 0.6) = 330 room nights, so the suggested block is 330 × 90% = 297 room nights. With a 20% attrition allowance the group must pick up 297 × 80% = 237.6, so at least 238 room nights. If nobody booked, the guarantee would be 237.6 × $219 = $52,034, and each room night short of the floor costs $219. The block earns about 5 comp room nights at 1 per 50.

Sources: Cornell Law School LII: Liquidated damages (the legal basis of attrition clauses) · Engine: Hotel attrition calculator for group room blocks (cumulative and per-night formulas, resale credit) · Mews: Hotel attrition, clauses and worked fee example

Frequently asked questions