NIFTY lot size change: one symbol, two lot sizes, and how a revision reaches contracts that already exist
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A NIFTY lot size change does not restamp contracts that already exist. Three dates decide which lot applies: announced, effective and fully effective.
A NIFTY lot size change does not reach every contract on one day. During the revision window, "What is the NIFTY lot size?" does not have one answer. A lot size is part of a contract's specification. An exchange cannot change it on contracts that already exist. Doing that would change the size of positions people already hold. Instead it applies the new lot to newly introduced contracts, and lets the old ones run to expiry. That is how one index legitimately trades at two different lot sizes at the same time, for weeks.
- Three dates matter, not one. The first is when the circular was published. The second is when the new lot starts applying. The third is when the last contract on the old lot has expired.
- During that window, two live contracts on the same index carry different quantities per lot.
- A table that stores one lot size per symbol is wrong for the whole window. It is also wrong in a way that looks authoritative.
- When a notice names no single completion date, the table here says so instead of inventing one.
A lot size is a contract term, not a display setting
The lot size is the quantity of the underlying that one contract stands for. It is written into the contract specification, and it sets what a position is worth. Change it on a contract somebody already holds, and you have changed their position size without them trading.
So exchanges do the only workable thing. The revised lot applies to contracts introduced after a stated date. Contracts that already exist keep the lot they were born with until they expire. The revision reaches the market slowly, as the old contracts run off.
NIFTY lot size change: the three dates that matter
The October 2025 NSE index revision is a clean example. It is also the one behind the numbers on this site's lot-size table.
| Symbol | Lot before → after | Circular dated | Applies to newly introduced contracts from | Every live contract carries it from |
|---|---|---|---|---|
| NIFTY (Nifty 50) | 75 → 65 (−13.3%) | 3 October 2025 | 28 October 2025 | 31 December 2025 |
| BANKNIFTY (Nifty Bank) | 35 → 30 (−14.3%) | 3 October 2025 | 28 October 2025 | 31 December 2025 |
| FINNIFTY (Nifty Financial Services) | 65 → 60 (−7.7%) | 3 October 2025 | 28 October 2025 | 31 December 2025 |
| MIDCPNIFTY (Nifty Mid Select) | 140 → 120 (−14.3%) | 3 October 2025 | 28 October 2025 | 31 December 2025 |
| NIFTYNXT50 (Nifty Next 50) | unchanged at 25 | 3 October 2025 | 28 October 2025 | 28 October 2025 |
Read from the circular's own wording: The circular came into effect from 28 October 2025 EOD. Weekly and monthly contracts that already existed kept the old lot until the 30 December 2025 expiry, and existing quarterly and half-yearly contracts were revised at 30 December 2025 EOD — so every live contract carried the revised lot from 31 December 2025.
Between the effective date and the completion date, both lots are correct. "What is the lot size" is not a full question. It needs "on which date, for which contract".
Why lots get revised at all
Index derivative contract sizes are kept inside a value band of ₹15–20 lakh. An index level moves over time, so a contract's value can drift out of that band. That drift is why lots are revised. It is not because of anything that happened on the day of the circular.
The arithmetic makes that concrete. It does not claim where the index actually traded. Take an index level of 27,000. One NIFTY contract at the old lot of 75 would be worth ₹20.25 lakh. That is above the ₹20 lakh ceiling of the band. At the revised lot of 65, the same level gives ₹17.55 lakh, back inside it.
What the window does to arithmetic done by hand
Multiply the quoted premium by the contract's lot size to get the rupee amount. During a transition, two contracts of the same index can have the same quote but different quantities. Their total premiums will differ.
- Charges are levied on premium turnover, so they follow the quantity. A cost estimate worked out with the wrong lot is wrong by the ratio of the two lots.
- The same applies to any per-lot figure worked out by hand. Each one inherits the lot that was assumed.
- The contract's own specification, not the newest circular, is what governs the contract in front of you.
When the notice names no completion date
SENSEX shows the other case. The notice revises the market lot for contracts introduced after 20 November 2024. Unexpired November 2024, December 2024 and January 2025 monthly contracts kept the old lot until their own expiry, and long-dated contracts changed at 27 December 2024 EOD.
The notice gives three different run-off dates rather than one. No single date exists on which every live contract carried the revised lot. This site's table reports that the completion date is not stated. It does not pick the latest of the three and present it as fact.
The absence of a date is information. A reference table with a value in every cell is telling you things it does not know.
How to find the new lot size of NIFTY
- Decide the date that matters. It is the date the contract was introduced, not today.
- Take the record whose effective date is the latest one on or before that date. Not the newest record in the table.
- Check whether that date sits inside a transition window. If it does, the contract in hand may still be on the older lot.
- Confirm against the circular itself before anything depends on the number.
That is exactly what the lot-size page on this site does. The same records are also published as machine-readable JSON. Each carries its announced, effective and last-verified dates. A program can apply the same rule.
What this site deliberately does not publish
- An expiry calendar. Expiry assignments are set by their own circulars, and were revised more than once during 2025. A wrong answer to "which day does this expire" is the answer that gets quoted. The market hours page shows only the next monthly expiry for NIFTY and BANKNIFTY.
- Single-stock F&O lot sizes. That is roughly two hundred symbols, each on its own revision cycle. Publishing them unverified is the mistake the lot-size page exists to avoid.
The documents this post is built on
Each card is a real document, named by its own reference number and date, with the part of this post that rests on it and the day a human last opened it.
Lot sizes, announcement date, effective date and the run-off wording for NIFTY, BANKNIFTY, FINNIFTY, MIDCPNIFTY, NIFTYNXT50.
The SENSEX lot revision and its three separate run-off dates. BSE publishes notices by number rather than at a stable document address, so no link is cited.
Sources
If a figure here disagrees with its source, trust the source.
Make it concrete
Frequently asked
Can two contracts on the same index really have different lot sizes?
Yes, during a transition window. Contracts introduced after the effective date carry the revised lot. Contracts that already existed keep the old one until they expire.
Which lot size applies to the contract I am looking at?
The one in force when that contract was introduced. Take the record with the latest effective date on or before that date. Then confirm it against the circular.
Why do lot sizes change?
Index derivative contract sizes are kept within a value band of ₹15–20 lakh. As an index level moves over time, the contract value can drift out of the band. The lot is then revised to bring it back.
Does this site publish expiry days?
No expiry calendar. The page about whether the market is open today shows the next monthly expiry for NIFTY and BANKNIFTY, and the Option Premium Market X-Ray shows the expiries it compares. Both are worked out from NSE's expiry rule and holiday list. Expiry weekday rules come from their own circulars, and they changed more than once during 2025. Check NSE's own notice before you rely on an expiry date.
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Every row with its circular, effective date and the date it was last checked.