Author: Tradetron Team | Reviewed by: Tradetron Team | Published: 30 August 2026 | Last updated: 30 August 2026
Quick answer
From the January 2026 contract series, the Nifty 50 lot size is 65 units (down from 75) and Bank Nifty is 30 (down from 35). Nifty Financial Services moved from 65 to 60 and Nifty Midcap Select from 140 to 120. Nifty Next 50 stayed at 25. If you run automated strategies, changing the lot count is not enough. Anything expressed in rupees rather than lots now behaves differently.
Most coverage of this change stopped at the table. That is the easy part, and by now most traders know the numbers.
The part nobody wrote is what happens to a strategy that was already deployed when the change landed. A running strategy does not just have a lot count. It has stop-losses in rupees, position sizing formulas, margin assumptions, hedge ratios and a backtest history, and several of those quietly mean something different now than they did in December. If a strategy of yours has been sitting dormant, or trades only on certain setups, or you inherited it from the marketplace, it is worth an hour of your attention.
What are the new lot sizes?
NSE announced the revision in a circular in late November 2025, effective from the January 2026 series.
The transition worked on expiry, not on a calendar date. December 2025 contracts ran to expiry under the old sizes, with the 23 December weekly the last of them. The new sizes showed up in the 6 January 2026 weekly expiry and the 27 January monthly. Quarterly and half-yearly contracts adopted the new sizes from the end of 30 December 2025.
Lot sizes are set so that a single contract's notional value stays inside the range SEBI's framework allows. As an index rises, contract value rises with it, and eventually the exchange trims the lot to bring it back. NSE reviews this periodically, so treat the numbers above as current rather than permanent.
What it means in rupees
At a Nifty level around 26,000, one lot represented roughly Rs 19.5 lakh of notional exposure before. It now represents about Rs 16.9 lakh. Bank Nifty around 58,000 moved from roughly Rs 20.3 lakh to Rs 17.4 lakh per lot.
Two consequences follow, and they run in opposite directions.
Margin per lot fell, which lowers the entry barrier and gives you finer control over position size. That is the intended benefit.
Per-point profit and loss also fell. A one-point Nifty move is now Rs 65 per lot instead of Rs 75. On Bank Nifty it is Rs 30 instead of Rs 35. If you were running a strategy sized to produce a certain rupee outcome, it now produces about 13 percent less on the same number of lots.
That is the whole explainer. The rest of this article is the part that actually costs people money.
The settings to check on a running strategy
Work through these in order. The first two are obvious and most people did them in January. The rest are the ones that get missed, and several of them fail silently, meaning the strategy keeps running and simply behaves differently from what you validated.
1. Is your quantity expressed in lots or in units?
Check this first, because it determines how much of the rest applies to you.
A strategy that specifies quantity in lots will pick up the new contract size automatically, because the exchange defines what a lot contains. A strategy that specifies an absolute unit count, or that has 75 or 35 written into a formula somewhere, will not. It will keep asking for a quantity that no longer maps cleanly onto a whole number of contracts.
Open each deployed strategy in the Tradetron strategy builder and search the position legs and any sizing logic for hardcoded numbers. Old values of 75, 35, 65 and 140 are the ones to look for, and note that 65 is ambiguous now, since it is simultaneously the old FinNifty lot and the new Nifty lot.
2. Your total exposure changed even though your lot count did not
This is the one that surprises people who did check their settings.
If you were trading 4 Nifty lots, you had 300 units of exposure. The same 4 lots now give you 260. You did not change anything, and you are running 13 percent smaller than you were.
The awkward part is that you cannot get back to 300. Five lots is 325 units, which is 8 percent more than you had, not 13 percent less. Lot sizes are a granularity constraint, and on a smaller lot the granularity is finer but the arithmetic still does not land exactly where you were.
Decide deliberately which one you want: hold lot count and accept lower exposure, or hold exposure and accept a step up. Do not leave it as an accident. If your strategy sizes positions off available capital rather than a fixed lot count, confirm the formula is reading the current contract size rather than a value captured when you built it.
3. Rupee-denominated stop-losses now trigger at a different point move
This is the single most consequential item on the list, and it is invisible in the interface. Nothing looks wrong.
Say you set a stop-loss of Rs 5,000 per lot. Under the old lot size, that was a move of 66.67 Nifty points. Under the new one, the same Rs 5,000 is 76.92 points.
Your stop got wider. Not because you widened it, but because each point now costs less. A strategy that was designed to cut a losing trade at roughly 67 points against it will now sit through 77 before acting.
The reverse applies to point-based stops. A 60-point stop that used to represent Rs 4,500 of risk per lot now represents Rs 3,900. Your risk per trade fell by 13 percent, which sounds harmless until you realise your position sizing model was probably calibrated against the old figure.
Go through every rupee-denominated value in the strategy and decide whether you want to preserve the rupee amount or the point equivalent. They are different decisions and only you know which one your strategy's logic actually depends on. The same applies to targets, trailing stop triggers and trailing step sizes.
4. Strategy-level maximum profit and maximum loss
If you set a daily maximum loss or a maximum profit at the strategy level, those are rupee figures sitting on top of a position that now moves 13 percent less per point.
A max loss that used to be hit by roughly a two-lot adverse move of a given size now needs a larger move to trigger. In practice your circuit breaker is looser than it was. Recalculate it against the new per-point value rather than leaving the number you set last year.
5. Cross-index hedge ratios are now mismatched
Almost nobody covers this, and it is the sharpest trap in the whole change.
The four indices were not cut by the same percentage. Nifty came down 13.33 percent. Bank Nifty and Midcap Select came down 14.29 percent. FinNifty came down only 7.69 percent.
If you run any strategy that balances exposure across two different indices, a Nifty position hedged against a Bank Nifty position, or anything pairing Nifty with FinNifty, the ratio you carefully calibrated is now off. The Nifty and FinNifty pairing is the worst of them, with almost six percentage points of drift between the two legs.
Recompute the ratio from the new unit counts. Do not assume that because both indices got smaller, the relationship held.
6. Multi-leg option structures and premium collected
For option sellers the arithmetic is straightforward and slightly unwelcome. You collect premium on fewer units, so income per lot falls proportionally. Getting back to the same rupee income means more contracts, which means more transaction cost and more slippage.
Slippage is worth doing the sum on rather than waving at. Two legs, one lot, one and a half rupees of slippage per leg comes to 2 × 65 × Rs 1.50, or Rs 195 per entry. Run that daily across a month and it is close to Rs 3,900 before you account for anything else. If you scale up lots to restore your old income, scale that number too.
If you use Overnight Protection, check the hedge leg specifically. It buys a hedge ahead of the session close and exits it the next trading day. Confirm the hedge quantity still lines up with the position it is protecting, because a ratio you set last year was set against a different unit count.
7. Backtests run before January 2026 describe a different instrument
Any backtest result you are relying on that was generated before the change reflects the old contract size. The percentage returns are broadly still informative. The absolute rupee figures, the drawdown in rupees, the per-trade profit and loss, and anything you derived from them are not.
Re-run the backtest on FastBT before you use it to justify a capital allocation. This matters most for the strategies you are least likely to touch, the ones that have been quietly profitable and that you therefore have no reason to open. For the full list of reasons a backtest and a live strategy can diverge even before you account for a lot-size change, see Why Your Backtest Doesn't Match Live Trading.
While you are re-running, read the result the way you should always read one. Fill assumptions and slippage sit between a backtest and reality regardless of lot size.
8. External signals and any quantity you send in
If a strategy is driven by signals from an external tool, and that tool passes a quantity, check what it is passing. A webhook that sends a unit count rather than a lot count is a live mis-sizing waiting to happen, and it will not announce itself.
9. If you publish strategies to the marketplace
Your subscribers' capital requirement changed, and so did the minimum capital your strategy needs to run at one lot. If your strategy page states a minimum capital figure or an expected return in rupees, both are now out of date. Subscribers running a multiplier are affected in the same way you are.
10. Re-validate in paper trading before you trust it
After you have adjusted a strategy, run it in paper trading and watch it take a few real positions on live data. Confirm the quantity that actually goes out matches what you intended, and that stops trigger where you now expect rather than where they used to.
This is the step people skip because the changes felt small. The changes were small individually. Compounded across sizing, stops and hedge ratios, they are not.
Why the lot size changes at all
SEBI's framework sets bounds on the notional value of a single derivatives contract. As an index climbs, the value of one contract climbs with it, and a lot that was appropriately sized three years ago eventually represents more exposure than the framework intends for a single unit of trade.
NSE calculates the revision from the average closing price of the underlying over a reference period. For this revision, that period was September 2025.
The practical implication for anyone running systematic strategies is that this will happen again. Build a habit rather than doing a one-off migration: when a lot size revision is announced, run the ten checks above rather than only updating the lot count.
A note on when this actually became live
The change was announced in November 2025 and took effect from the January 2026 series. If you are reading this well after that, you might reasonably assume it no longer applies to you.
It applies to any strategy you have not opened since then. Dormant strategies, seasonal ones, strategies that only fire on specific setups, and anything you subscribed to and left running are all candidates for having stale rupee values inside them. The lot count updated itself. The stop-loss in rupees did not.
Frequently asked questions
What is the Nifty lot size now?
The Nifty 50 lot size is 65 units, effective from the January 2026 contract series. It was previously 75 units.
What is the Bank Nifty lot size now?
The Nifty Bank lot size is 30 units, effective from the January 2026 contract series. It was previously 35 units.
When did the new lot sizes take effect?
They took effect from the January 2026 series, after the December 2025 contracts expired. The new sizes applied from the 6 January 2026 weekly expiry and the 27 January 2026 monthly expiry.
Did FinNifty and Midcap Nifty lot sizes change too?
Yes. Nifty Financial Services moved from 65 units to 60, and Nifty Midcap Select from 140 units to 120. Nifty Next 50 remained unchanged at 25.
Do I need to change the lot size in my algo strategy manually?
If your strategy specifies quantity in lots, the contract size updates automatically. If it specifies an absolute unit count, or has the old lot size written into a sizing formula, you need to update it manually.
Does a lot size change affect my stop-loss?
Yes, if your stop-loss is set in rupees. A Rs 5,000 per-lot stop was a 66.67 point Nifty move under the old lot size and is a 76.92 point move under the new one, so the effective stop is wider.
Is my total exposure the same if I keep the same number of lots?
No. Four Nifty lots was 300 units before and is 260 units now, about 13 percent less exposure for the same lot count.
Are my old backtest results still valid?
Percentage-based results remain broadly informative, but absolute rupee figures such as per-trade profit, loss and drawdown reflect the old contract size. Re-run the backtest before using it to size capital.
Did the lot size change reduce margin requirements?
Yes. A smaller lot means lower notional value per contract and therefore lower margin per lot, though per-point profit and loss falls proportionally as well.
How much is one Nifty point worth per lot now?
One index point is worth Rs 65 per Nifty lot and Rs 30 per Bank Nifty lot, down from Rs 75 and Rs 35 respectively.
Do hedge ratios between two indices need recalculating? Yes. The indices were reduced by different percentages, from 7.69 percent for Nifty Financial Services to 14.29 percent for Nifty Bank, so any position balanced across two indices is now mis-ratioed.
Why does NSE change lot sizes? Lot sizes are revised so the notional value of a single contract stays within the range SEBI's framework allows. As an index level rises, contract value rises with it, and the exchange periodically trims the lot to compensate.