How IPO GMP Is Calculated

Where a grey market premium figure comes from, how the expected listing price and gain are worked out from it, why different sites show different numbers on the same day, and what the record says about how well it predicts the listing.

Published 14 September 2026 · IPO Sahayak

Every GMP page — including ours — shows a single rupee figure per IPO as if it were a price printed by an exchange. It is not. It is a number collected from a handful of people, at a particular hour, that has been rounded, averaged or simply repeated by the time it reaches a website. This guide explains how that number is produced, how the figures derived from it are worked out, and what the last few years of listings say about how much weight it deserves.

Where the raw number comes from

The grey market is a dealer network, not a venue. Dealers — concentrated in a few cities, historically Ahmedabad, Rajkot, Mumbai and Kolkata — quote a price at which they will buy or sell shares of an IPO that has not yet listed. The quote is a premium over the issue price, in rupees per share, and it changes through the day as the dealers' own positions change.

Nobody records these quotes centrally. What a website publishes is one of three things: a figure a dealer contact gave them on the phone or over a messaging app, a figure copied from another site that got it that way, or an average of a few such figures. There is no timestamp on most published numbers and no way to check them after the fact. This is the single most important thing to understand about GMP — the number is a report, not a record.

The arithmetic behind the derived figures

Three numbers get built on top of the raw premium, and the formulas are simple enough to check yourself.

Expected listing price

Issue price (the upper end of the band, or the final price once announced) plus the GMP. An issue at ₹300 with a premium of ₹45 implies a listing around ₹345.

Expected listing gain

GMP divided by the issue price. ₹45 on ₹300 is 15%. Note that sites quote the premium in rupees and the gain in percent, and the two are often shown side by side — a ₹45 premium sounds larger on a ₹300 issue than the same ₹45 does on a ₹900 issue, where it is 5%.

Expected profit per lot

GMP multiplied by the lot size. With a lot of 50 shares, ₹45 becomes ₹2,250 per lot. This is the figure that gets quoted most loudly and is the least meaningful, because it assumes you are allotted a lot, that you sell at exactly the implied price, and that the premium holds until listing. None of those is guaranteed.

Why two sites show different numbers on the same day

• Different dealers. Quotes vary between dealers by a few rupees at any moment, the way two currency changers on the same street quote slightly different rates.
• Different times. A figure collected at 11 am and one collected at 6 pm on a day when subscription numbers were published in between can differ a lot.
• Copying with a lag. Many sites republish another site's figure, sometimes a day late. The result is a number that looks stable when the underlying market has already moved.
• Rounding. A premium quoted as “₹40–45” by a dealer becomes 40 on one site and 45 on another.

A spread of ₹5–10 between sources on a mainboard issue is normal. A spread wider than that usually means one of the sources is stale.

What actually moves the premium

The premium responds to a few observable inputs, roughly in this order of weight:

1. QIB subscription on the final day. Institutional bids come in late and cannot be withdrawn after close, so the day-three QIB number is the strongest single input. A premium that survives a weak QIB book is rare.
2. The overall subscription multiple, and particularly the retail and HNI numbers, which determine how hard the shares will be to get and therefore how much dealers can charge for them.
3. The Nifty and the sector. A 2% fall in the index between close and listing routinely takes a third or more off a premium.
4. Dealer inventory. Dealers who have bought heavily have an interest in a high quote during the subscription window and in unloading before listing. Because volumes are small, a few trades move the figure.

What the record says about reliability

The honest summary is: right on direction more often than not for large, well-subscribed mainboard issues; unreliable on magnitude everywhere; and close to noise for SME issues and for anything heavily hyped. A few patterns repeat across listings:

• Premiums tend to overstate the eventual gain. An issue quoting a 40% premium a week before listing far more often lists at 20–30% than at 40%.
• The last two trading days before listing carry the largest revisions. A figure from the middle of the subscription window is of little use on listing morning.
• Small premiums (under 5% of issue price) have very little predictive value in either direction — those issues list flat, up or down with roughly the same frequency.
• Issues carrying a strong premium have listed below their issue price. It is not common, but it happens every year, usually when the broad market drops between close and listing.

Our closed IPO page lists issue price against actual listing price for past issues. Comparing that to the premium those issues were quoting in their final week is the most useful exercise you can do before trusting a GMP figure on a live issue.

A sensible way to use the number

Treat GMP as a reading of sentiment among a small group of professional speculators, and weigh it against things that can be verified:

• The category-wise subscription figures, and especially the QIB number on the final day.
• The valuation section of the RHP — the price-to-earnings the issue is asking for against the listed peers it names. See how to read an RHP.
• How much of the issue is an offer for sale, which tells you whether existing holders are cashing out at this price. See fresh issue vs OFS.

If those three point one way and the premium points the other, the premium is the thing to doubt. For the background on the grey market itself — who the dealers are and why none of it is regulated — see what IPO GMP actually is.

Common questions