Bid Price vs Ask Price

The bid price is the highest price any buyer in the market is currently offering for a share; the ask price is the lowest price any seller is currently willing to accept. The ask sits above the bid whenever a stock is trading normally, and the gap between the two — the bid-ask spread — is what dealing immediately costs.

Both numbers come straight out of the exchange's order book. On the NSE and BSE, every limit order that has not yet found a match waits in that book: buy orders queued on one side, sell orders on the other. The best bid is simply the top of the buy queue, and the best ask is the top of the sell queue. Nobody sets these prices — not the exchange, not SEBI, not your broker. They are the live intentions of other market participants, and they move every time an order is placed, matched, modified or cancelled.

Why does the ask price sit above the bid?

Because any overlap is traded away the instant it appears. The exchange's matching engine exists to pair compatible orders: the moment a buyer offers what a seller is asking, the two orders execute and both leave the book. Whatever remains on screen is, by definition, the set of orders that could not yet be matched — buyers bidding less than the cheapest seller demands. The best bid and the best ask are simply the two closest unfilled positions on either side of that divide.

This makes the spread a living number rather than a fixed property of the stock. Every new limit order placed inside the old gap narrows it; every cancellation at the top of the book can widen it. In a heavily traded large-cap, buyers and sellers leapfrog each other all day by the smallest increment the exchange permits, and the gap stays compressed. In a neglected counter, the two sides can sit far apart for hours because nobody finds it worthwhile to close the distance.

What the market depth window on your broker app shows

Tap on any stock in a broker app and behind the headline price sits the market depth view. On an NSE quote this typically displays the five best bid levels and the five best ask levels, each with a price and the quantity resting at it, along with the total buy and sell quantity across the book. The top row of the buy side is the best bid; the top row of the sell side is the best ask; every deeper row is an order that was outbid or undercut by someone more competitive.

Each of those rows is built from resting limit orders — the patient half of the market waiting for its price. How your own order behaves when it arrives depends entirely on the type you choose, which is the territory of market orders vs limit orders: one joins the queue, the other consumes it. Treat the displayed quantities with mild suspicion either way. An order can be cancelled or modified in a fraction of a second, and the exchange also permits disclosed-quantity orders that reveal only part of their true size — so the depth window can overstate real interest and understate it at the same time. It is a photograph of a moving object.

The spread is a trading cost, even though nothing bills you for it

Suppose a share shows a best bid of ₹99.50 and a best ask of ₹100.50. Buying immediately means paying ₹100.50; selling that same share immediately afterwards means accepting ₹99.50. The round trip surrenders ₹1 per share — one percent on a ₹100 stock — with the price itself having gone nowhere. That rupee did not vanish into fees; it was transferred to the counterparties who were quoting patiently on both sides of the book.

No contract note will ever show it. Brokerage, securities transaction tax and the exchange and statutory levies are all itemised, and you can total the visible ones for any trade with the trading charges calculator — but the spread is paid silently, embedded in the execution price. Measured against the midpoint of the two quotes, each side of a round trip bears half the spread. The cost also repeats on every trade, which is why the same spread weighs far more heavily on an account that turns over daily than on one that transacts occasionally.

The same absolute spread also costs different amounts at different price levels, which is why it belongs in percentage terms. A gap of five paise on a share quoting near ₹1,000 is a rounding error; the identical five paise on a share quoting near ₹10 is half a percent of the price on every crossing. Low-priced and thinly traded shares often combine the two problems — a wide spread sitting on a small price — so the proportional cost of impatience there can dwarf every visible charge on the trade.

What happens if you place an order between the bid and the ask?

You become the market. Place a limit buy above the current best bid but below the ask, and your order is now the best bid on the exchange — first in line, with the spread narrower than it was a second ago. NSE and BSE match on price-time priority: a better price always ranks ahead, and among orders at the same price, the earlier one fills first. Your improved bid now waits for a seller willing to come down to it, and there is no guarantee one will.

The alternative is to cross the spread yourself: buy at the ask or sell into the bid and be done instantly. If your quantity is larger than what rests at the best level, the balance walks deeper into the book, filling at successively worse prices until it is done. That slippage on size is the beginning of impact cost, and it is the practical reason the quantities in the depth window matter as much as the prices.

One quirk of the queue is worth knowing early: priority is earned, and it can be forfeited. Change the price of a resting order and it re-enters the queue on a fresh timestamp, behind everyone already waiting at that level. A trader who keeps nudging a limit order towards the market is repeatedly surrendering their place in line — often ending up, after several revisions, simply paying the spread they set out to avoid.

Why the last traded price is not a price you can trade at

The number on your watchlist is the last traded price — the price at which the most recent match happened. It is a record of the past, even if the past is only milliseconds old. The prices actually available to you are the current best ask if you want to buy and the current best bid if you want to sell, and both can differ from the LTP the moment you look.

In a liquid large-cap the three numbers cling together, refreshed many times a second, and the distinction feels academic. In a thinly traded counter it is anything but: the last trade may have printed hours ago, and the quotes may have drifted a long way since. A sparse number of trades through the day is the tell. A stock showing a comfortable-looking LTP above a gaping spread is telling you which of its numbers to believe — and it is not the one on the watchlist.

How tick size puts a floor under the spread

Prices on an exchange do not move continuously; they move on a grid. The tick size is the minimum price increment the exchange permits, and every bid and ask must land on a multiple of it. The spread therefore has a hard floor of one tick — the best bid and best ask can never sit closer than that without matching. In the most heavily traded shares, competition presses the spread down to or near this minimum, which is as tight as market structure allows it to get.

The tick schedule itself is set by exchange circulars, differs across price levels and segments, and has been revised over the years — so treat the exact values as something to check on the NSE or BSE website rather than memorise. The mechanism is what matters: a finer tick lets quotes compete in smaller steps and can narrow spreads in liquid names, while a coarser tick fixes a wider minimum gap no matter how much interest there is.

When do bid-ask spreads widen on NSE and BSE?

A spread is the price of standing still in public. Anyone resting a firm quote is granting every other participant a free option to trade against it, and when the risk of being caught on the wrong side rises, quotes are widened or withdrawn. The situations that widen spreads all share that one mechanism.

• At the open, while the book rebuilds after the pre-open call auction and participants test where the day's interest actually lies.
• Around results, announcements and sharp news, when whoever keeps quoting risks being picked off by someone who has read the headline first.
• In small-cap and SME-platform counters, where few participants quote at all and the two sides sit naturally far apart.
• When a large order sweeps the book faster than fresh quotes replace what it consumed.

Price bands produce the extreme case. When buying pressure pins a stock at its upper band, the sell side of the book can empty entirely — buyers queue at the maximum permitted price and there is no ask at all; the mirror image happens at the lower band. How those bands and their trading halts work is covered in circuit limits; for reading quotes, the point is that a missing side of the book is information, not a display error.

What the spread tells you about liquidity — and what it cannot

A narrow spread backed by genuine quantity is the signature of a liquid market: orders of ordinary size can enter and exit with little slippage. This is precisely what impact cost measures, and low impact cost is among the liquidity standards used for index selection in India. But the spread alone is not enough — a tight quote resting on a handful of shares is a veneer, which is why it should be read together with depth and with volume and turnover across the day.

What the spread cannot tell you is anything about the business behind the ticker. A stock that is cheap to trade is not therefore cheap to own; a tight spread reflects competition among traders, not the quality of the company's earnings. Nor is an imbalance between displayed buy and sell quantity a dependable directional signal — resting interest can be cancelled in an instant, and what is displayed is whatever its owners want displayed. The spread describes the market for the share, never the merit of the share.

Reading the quote screen before your first order

The two quotes reward a short ritual before any order, and it takes seconds once it becomes habit.

1. Locate the best bid and best ask, and work out the spread both in rupees and as a percentage of the price.
2. Compare the quantity resting at the best levels against the size you intend to trade, and glance at the deeper rows rather than only the top of the book.
3. Check how recent the last traded price is, and whether it sits inside or outside the current quotes.
4. Look at the total buy and sell quantities for a sense of how one-sided the book is, remembering that displayed interest is provisional.
5. Choose the order type with the spread in front of you — a limit order fixes your price, a market order fixes your execution.

Everything around that moment — opening the account, funding it, what happens on settlement day — is walked through in how to buy your first share. The quotes themselves ask for something simpler: the habit of looking at both numbers. The bid and the ask are written by strangers, updated in real time, and honest in a way headlines are not — between them sits the only market that will actually take your order.