Basis of Allotment or Basis of Allocation is a document publishes by registrar of an IPO to stock exchanges and IPO investors. This document provides information about final price fixed for an IPO, issue subscription (bidding) information or demand of an IPO and share allocation ratio.

The IPO allotment information is categorized by number of shares applied by an applicant. For each such category detail bidding information is provided in this document including number of valid application received, total number of share applied, ratio of the allotment and number of shares allocated to the applicants.

Ratio of the allotment is a critical field for IPO's oversubscribed multiple times. This field tells how many applicants will receive single lot of shares among a certain number of applicants. For example, ratio 1:8 means only one out of eight applicant received one lot of shares; ratio value 'FIRM' means all the applicants are eligible to receive certain amount of share.