Exchanges publish subscription figures during the issue period, usually updated several times a day and finalised after the issue closes.
High retail subscription reduces the chance of receiving an allotment, because shares must be distributed among more applicants.
An easy example
If 1 crore shares are offered and applications arrive for 4 crore shares, the issue is subscribed 4 times.
Important note
Subscription is reported separately for institutional buyers, non-institutional investors, retail investors and employees.
Common mistake
Reading high subscription as proof that an IPO will do well after listing. It measures demand during the issue, nothing more.