Guide · Risk and sizing · Stage 1

Position sizing for Indian retail traders: the practical method

Position sizing is the one part of trading that is pure arithmetic, and the one part most retail accounts get backwards. Almost everyone decides how many to buy from how much capital they have or how confident they feel, then places a stop wherever leaves room. That is sizing by comfort. The disciplined order is the reverse: the market decides where your stop belongs, your risk budget decides how much you will lose if it is hit, and only then does the quantity fall out. This page is the hands-on version of that idea, on the instruments Indian retail actually trades, including the structural reason the maths simply refuses to work below a certain account size.

The formula, and why it runs in this order

Three inputs produce a position size, and the order they are fixed in is the whole discipline. Reverse the order and you get the behaviour that empties accounts.

Written plainly, the rule is quantity = (account equity × risk fraction) ÷ stop distance per unit. Each input earns its place:

1. Account equity, measured as today's current equity, not the balance you started with and not last month's peak. Sizing off a stale number is how risk quietly drifts.
2. Risk fraction, a small pre-committed slice of that equity, decided before you look at any chart so conviction cannot inflate it.
3. Stop distance, the rupees between your entry and the level that says the idea was wrong. This comes from structure, not from the size you would like to hold.

The third input is the one that gets reversed. The common mistake is to decide the position first, say a round two lakh rupees, then set the stop at whatever distance makes the loss look tolerable on that size. That is sizing by comfort, and it detaches the stop from the chart, which is the one place it can carry information.

Why risk must be a fraction of current equity

Fixing risk as a percentage of live equity rather than a flat rupee amount is not a stylistic choice; it changes the mathematics of survival. A fixed fraction shrinks your rupee risk automatically after a run of losses, because the equity it is computed on has fallen, and lets it grow after gains. This is what keeps a losing streak from compounding into ruin: each loss makes the next bet smaller, so the account decays geometrically toward zero without ever mechanically reaching it, instead of marching there in fixed steps.

A flat rupee risk does the opposite in both directions. Hold the risk at a fixed 2,000 rupees while the account falls from two lakh to one lakh, and that 2,000 has silently doubled from one percent of equity to two percent, accelerating the decline precisely when you can least afford it. Let the account grow to eight lakh while you still risk 2,000, and you are now risking a quarter of one percent, leaving return on the table for no gain in safety. The fraction self-corrects for both; a rupee figure corrects for neither. The discipline is to recompute the budget from current equity before every trade, which is the subject of the sizing tools in the position-sizing calculator.

Stop distance sets the size, not conviction

Because rupee risk equals quantity multiplied by stop distance, and you are holding rupee risk fixed, the stop distance and the position size move in strict inverse proportion. A wider stop forces a smaller position; a tighter valid stop allows a larger one. Nothing about how strongly you believe in the trade enters the arithmetic. This is the single most useful thing sizing teaches, and the one most often ignored.

The practical consequence is that stop distance and volatility, not enthusiasm, govern how large you can be. An instrument whose honest invalidation sits far from entry has to be traded small; one where a tight level genuinely invalidates the idea can be traded larger for the same rupee risk. If the quantity the formula returns feels too small, the correct responses are to find a tighter valid entry, or to accept the smaller size. The response that ends accounts is to widen the risk budget so the position feels right, because that quietly raises the loss you will take on every trade at once.

A worked grid makes the inverse relationship concrete. Every figure below is illustrative, chosen to show the arithmetic rather than to describe any real instrument.

Read across any row and the units fall as the stop widens; read down any column and they rise with equity. In every single cell, the rupee lost if the stop triggers is exactly the risk budget in that row. That invariance, the same rupee loss regardless of instrument or stop, is the entire point of sizing this way.

Cash equity versus F&O: continuous against lumpy

The formula is identical in both segments; what differs is whether its output can actually be traded. In the cash segment you buy whole shares and may hold as few as one, so quantity is effectively continuous. The formula might say 137 units and you can hold 137, matching your risk budget closely. Sizing in cash equity is a smooth dial.

In futures and options you do not trade units, you trade lots, and a lot is an indivisible bundle with a large fixed notional. Quantity therefore jumps in coarse steps: one lot, two lots, three, with nothing in between. If one lot already carries more rupee risk than your budget allows, there is no smaller legal size to fall back to. The formula still runs, but its answer, say 0.4 lots, cannot be filled, because fractional lots do not exist. Cash equity lets sizing be continuous; derivatives make it lumpy, and that lumpiness is not a nuisance at small account sizes, it is a wall.

The India scoop: the lot-size floor that breaks sizing

Here is the structural fact that dates most position-sizing advice written for an Indian audience. In October 2024, SEBI issued its framework to strengthen equity index derivatives, and from 20 November 2024 the minimum contract value for index derivatives was raised so that a new contract is introduced at no less than 15 lakh rupees, with the lot size set at each review so the contract value sits within roughly the 15 lakh to 20 lakh rupee band. Lots are whole numbers only; there is no fractional lot. Please verify the current lot size and band before trading, because the exchanges reset lot sizes periodically as prices move. As of the January 2026 series the Nifty lot is 65 units and the Bank Nifty lot 30, and with the Nifty near 24,400 in mid-2026 one Nifty contract is roughly 15.9 lakh rupees of notional, sitting inside that band.

Combine two hard constraints, one lot is the floor and one lot now carries a notional in the low tens of lakhs, and a small account meets a wall. The smallest position it can legally take already puts a rupee amount at risk that dwarfs any safe fraction of its equity. Proper position sizing is not merely difficult below a certain account size in this segment; it is arithmetically impossible.

The arithmetic is worth doing once, slowly. Take the Nifty, whose lot size is 65 units in the January 2026 series (verify the current lot before trading, as it is reset periodically). If your analysis puts a sensible stop 200 index points away, the rupee risk of a single lot is 200 points multiplied by 65, which is 13,000 rupees. On a 50,000 rupee account, a one percent risk budget is 500 rupees. The smallest position you can take risks twenty-six times what safe sizing permits: that trade alone puts 26 percent of the account on the line. Even a tight 100-point stop still risks 6,500 rupees, or thirteen percent of the account, on the minimum size. There is no quantity you can choose to fix this, because you are already at the floor.

This is not a fringe edge case. It is a plausible structural reason small derivatives accounts are chronically over-risked and prone to sudden ruin, and it sits underneath the regulator's own numbers. In its FY25 study released in July 2025, SEBI found that 91 percent of individual traders in the equity derivatives segment lost money, with aggregate net losses of about 1,05,603 crore rupees. Forced over-sizing is not the only driver, but an account that cannot mathematically size a single lot safely is an account starting from a losing structure. The linked breakdown of the SEBI F&O losses report sets those figures in context, and the mechanics of the lots themselves are covered in what a lot size in F&O actually is.

Fixed-fractional against the alternatives

Three sizing behaviours dominate retail accounts. Only one of them is position sizing; the other two are its imitations, and the last actively inverts it.

Fixed-quantity sizing, trading the same lot count or share count every time, feels tidy but lets rupee risk float free: a wider stop or a higher price silently raises the amount at stake, and nothing pulls it back. Averaging down is worse than uncontrolled, it is inverted. Adding units as the price falls increases quantity at the same moment the distance to any honest stop is growing, so rupee risk climbs precisely when the market is telling you the idea is wrong. It can feel like improving your average price, but arithmetically it enlarges the loss you are exposed to and dismantles the stop you set. Fixed-fractional sizing decides quantity once, from the stop and the budget, and never adds to a loser. That single restraint is most of what separates accounts that survive from accounts that do not.

Rebalancing size as equity changes

Because the whole method is anchored to current equity, sizing is not a one-time setup but a recurring recomputation. The rule is mechanical: before each trade, take today's equity, multiply by your fixed fraction to get the rupee budget, then divide by the trade's stop distance. Do not carry yesterday's rupee figure forward. An account that grew last week should be risking slightly more rupees this week for the same fractional risk, and an account that shrank should be risking fewer, automatically, without any decision to make.

This is also where the lot-size floor re-enters for anyone edging toward derivatives. As the account grows, there is a threshold at which one lot finally represents a safe fraction of equity, and only past that threshold does sizing in that segment have a valid solution at all. Below it, the correct position size in that instrument is zero lots, which is a legitimate answer the formula is allowed to give. Sizing that hands you zero is not the formula failing; it is the formula refusing to put you somewhere you cannot survive. Deciding where a stop belongs, and therefore whether a trade is sizeable at all, is upstream judgement, and that upstream work is exactly what the method we teach is built around.

Related reading

• Position sizing from first principles: why size is decided from risk
• Risk of ruin: the probability maths behind how often you go to zero
• What the SEBI F&O losses report actually shows