Bid-ask spread: the hidden fee on every options trade

You bought a SENSEX call. The screen said ₹119.50. One second later, before the index moved a single point, your position showed a loss.

Nothing broke. You just paid the spread.

Two prices, not one

An option does not have a price. It has two.

The bid is the highest price someone is currently willing to pay you for it. The ask (also called the offer) is the lowest price someone is currently willing to sell it to you for. The gap between them is the spread.

When you hit "buy at market", you buy at the ask. When you hit "sell at market", you sell at the bid. You are always crossing the gap, and you cross it twice — once going in, once coming out.

The airport money-changer

You have seen this board at the airport. USD BUY 87.20, USD SELL 89.60. The counter buys your dollars cheap and sells them dear, and the difference is their income.

If you changed ₹10,000 into dollars and immediately changed it straight back, you would walk away with noticeably less money. You did not lose it on the exchange rate. You lost it on the two-sided quote.

An options order book is the same board, refreshed a thousand times a second, run by market makers instead of a man behind glass.

What it actually costs on SENSEX weeklies

A SENSEX lot is 20 units. Strikes step in 100s. Prices move in ticks of ₹0.05, so a spread is always some whole number of ticks.

Take the example above: bid ₹118.00, ask ₹119.50, a spread of ₹1.50, which is 30 ticks.

• Buy 1 lot at the ask: you pay ₹119.50 × 20 = ₹2,390
• Sell that lot instantly at the bid: you receive ₹118.00 × 20 = ₹2,360
• Cost of the round trip: ₹30 per lot — before brokerage, STT, GST or stamp duty

Trade 5 lots and that round trip is ₹150. Take four such trades in a session and you have handed over ₹600 purely for the privilege of entering and exiting, with zero opinion about direction involved.

When the spread gets ugly

It is not a fixed number. It breathes, and it is widest precisely when retail traders are most tempted to click.

• Far out-of-the-money strikes. The cheap ₹4 lottery-ticket option that looks like a small bet often quotes ₹3.50 bid / ₹4.50 ask. That is a 25% round-trip cost. The strike has to move a quarter before you are even.
• The first few minutes after 9:15 AM. Market makers widen their quotes until the opening settles down.
• Thursday afternoon on expiry. As the clock runs out, quotes on anything away from the money get thin and jumpy.
• During a fast move. The instant the index rips, the book empties out. Your "market" order gets filled several ticks worse than the price you saw.
• Any non-standard strike. Stay near where volume actually sits. Thin strikes have wide quotes because nobody is competing for your order.

Reading the book before you click

Every broker terminal shows a depth window with the top five bids and asks, and the quantity sitting at each. Two habits are worth building.

First, look at the spread as a percentage, not in rupees. ₹1.50 on a ₹119 option is about 1.3%. ₹0.50 on a ₹4 option is 12.5%. The second one is far more expensive despite being the smaller number.

Second, look at the quantity at the best bid and ask. A tight ₹0.05 spread with 40 units on each side is not real depth. Your order eats through it and fills at the next level up.

Why this matters more than it looks

SEBI's own studies have found that the large majority of individual F&O traders lose money. Spread is not the whole explanation — but it is a real, measurable, every-single-trade leak that sits underneath every strategy, and most people have simply never added it up.

Do the arithmetic once for your own trading. Count your trades last month, multiply by lots, multiply by the typical spread on the strikes you actually use. The number is usually larger than expected, and unlike market direction, it is something you can see in advance every time you place an order.

Next time your position is red the instant it opens, you will at least know exactly who has it.