GMP decoded: what the grey market premium actually tells you

What the grey market is

Before an Indian IPO lists, its shares already trade — informally. Dealers in the grey market quote a price above (or below) the issue price at which they'll buy shares you expect to be allotted. That markup is the grey market premium (GMP): an IPO priced at ₹100 with a GMP of ₹25 is expected, by the street, to list around ₹125. Two cousins trade alongside it: the Kostak rate, a flat price for selling your entire application before allotment, and subject-to-sauda, the same deal but valid only if you actually get allotted.

None of this is official. There is no exchange, no clearing house, no regulator — just dealers netting off promises against each other. That's exactly why it's interesting: the GMP is the only forward-looking price an IPO has before it lists. The question is whether it's an honest one.

How accurate is GMP? We graded it.

Everyone quotes GMPs. Almost nobody grades them. So we do: for every IPO we track, we freeze the last grey-market quote before listing and compare it with the actual listing price — every outcome, no cherry-picking. At the time of writing that's 268 graded listings, and the scorecard runs live on the GMP Engine. The shape of the result:

• Direction: good. A positive GMP led to a positive listing roughly four times out of five. As a yes/no signal on "will it pop?", the grey market clearly knows something.
• Magnitude: mediocre. The median gap between the GMP-implied gain and the actual listing gain was about seven percentage points. A GMP is a rough estimate, not a forecast.
• Bias: it runs hot. The grey market systematically promises a little more than it delivers, and over-promised by more than five points on roughly one IPO in three. Dealers, subtly, are sellers of optimism.

Treat a GMP as a distribution, not a number. "GMP says +20%" really means "IPOs that said this listed anywhere from +11% to +27% half the time — and worse than that a quarter of the time."

That's why our IPO dashboard puts a "History says" column next to every live GMP: the actual range of listing outcomes for IPOs that carried a similar premium. The quote tells you what the street hopes; the history column tells you what happened to everyone who believed a similar quote before.

Where GMP lies

The grey market has one structural weakness: it's small, informal, and easiest to move exactly where retail attention is highest. In SME IPOs — tiny issues with tiny floats — a handful of coordinated trades can print a spectacular premium that no genuine buyer stands behind. The tell is a mismatch: a huge GMP sitting on top of weak real subscription numbers. Genuine enthusiasm shows up in both places at once; manufactured enthusiasm only shows up in the one that's cheap to fake.

Our IPO dashboard plots every live IPO on a premium-versus-demand map and flags that pattern explicitly. Big premium, thin demand, bottom-right of the map — that's where the manipulation lives, and it's the corner retail money gets invited into.

How to actually use it

• Use direction, distrust magnitude. A strong positive GMP with strong subscription is real information. The exact number is marketing.
• Check the base rate, not the quote. Look up what IPOs with a similar premium actually did — the calibration table exists so you don't have to take a dealer's word for it.
• Be paranoid in proportion to the float. The smaller the issue, the cheaper the premium is to fake. SME GMPs deserve roughly half your trust and twice your attention to subscription data.
• Never pay for it. Kostak and subject-to-sauda deals carry counterparty risk with no recourse. Reading grey-market data is free; transacting in it is not a market, it's a handshake.