Retail: a lottery once the book is oversubscribed
SEBI requires every retail applicant to get at least one lot. If retail bids exceed the retail quota, the registrar runs a computerised draw of lots — one lot per winning application, whatever size you bid. Applying for more lots doesn't improve your odds in an oversubscribed retail book; applying from more than one PAN (family members' own accounts) does. Duplicate applications under a single PAN are rejected outright.
NII (HNI): proportionate, with a minimum lot draw
The non-institutional quota is split between small NII (₹2–10 lakh bids) and big NII (above ₹10 lakh). Allotment there is proportionate to the bid, with a floor: when oversubscribed, every applicant is first eligible for the minimum application size by lottery, and anything left is shared pro-rata. In a hot issue, an NII bid can therefore be allotted a fraction of what was applied for.
The T+3 timeline
Since late 2023 mainboard IPOs list within three working days of closing. Day T is the close; the basis of allotment is finalised on T+1; on T+2 the unblocked amounts are released back to your bank (UPI/ASBA) and allotted shares are credited to your demat account; listing is on T+3. The dates on this page are the issue's own timetable, so a Sunday or an exchange holiday is already accounted for.
Three ways to find out
The registrar's status page (fastest, live from allotment evening); the BSE application check; or simply your bank — an SMS that the blocked amount was released means no allotment, while a demat credit alert means shares landed. Any site offering to "check allotment" for you by collecting your PAN is a phishing risk — the data lives only with the registrar.