How is the share allotment done?

P V Subramanyam, Trainer & Author, subramoney.com explains how share is allotment done.

After the closures of the issue, the bids received are aggregated under different categories i.e., firm allotment, Qualified Institutional Buyers (QIBs), Non-Institutional Buyers (NIBs), Retail, etc. The over subscription ratios are then calculated for each of the categories as against the shares reserved for each of the categories in the offer document. Within each of these categories, the bids are then segregated into different buckets based on the number of shares applied for. The over subscription ratio is then applied to the number of shares applied for and the number of shares to be allotted for applicants in each of the buckets is determined. Then, the number of successful allottees is determined. This process is followed in case of proportionate allotment. In case of allotment for QIBs, it is subject to the discretion of the post issue lead manager.