Position Size Calculator
How many shares or lots for a fixed rupee risk, what the trade pays after brokerage and STT, and — the part most calculators skip — how your risk per trade changes the odds of surviving the next hundred.
Charges come from the brokerage comparison; leverage costs from the MTF calculator. Computation only — not a signal.
The trade
Your account, how much of it one trade may lose, and the three prices.
1% is the usual ceiling
for the charges
Your edge — for the survival strip (win rate 45%, 1.8 R, 100 trades)
from your journal, not your hopes
of the starting account
Position size
Buy 166 shares — you risk ₹5,000 (1%) for a 2.0 R target
Reward ÷ risk: 2.00 R before charges, 1.78 R after at Zerodha
How this is worked out. Shares to buy = the rupees you are willing to lose ÷ the distance from entry to stop. The strip below then plays 100 trades at each risk level with your win rate, to show how often an account survives.
Position value
₹1.66 L
33% of account
If target hits
+₹9,565
after ₹395 charges
If stop hits
−₹5,359
after ₹379 charges
Survive 100 trades without a 50% drawdown?
0.5%
100%
worst drop 4%
1.0%
100%
worst drop 8%
2.0%
100%
worst drop 15%
3.0%
100%
worst drop 22%
5.0%
97%
worst drop 35%
Share of 2,000 simulated accounts that never fell to 50%, with the median worst drawdown, at a 45% win rate and 1.8 R. Same luck at every level. Your 1% is marked. Median ending equity at 1.0%: 1.28× start.
Twenty possible equity curves at 1% risk
Same win rate and R, different luck. The bold line is the median path; the red line is where the account counts as ruined.
- Survive at 0.5% risk
- 100%
- Survive at 1.0% risk
- 100%
- Survive at 2.0% risk
- 100%
- Survive at 3.0% risk
- 100%
45% win rate · 1.8 R · 100 trades · computation, not a signal · jpvfin.com
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The stop sets the size, not your conviction. Risk per trade in rupees divided by the distance to the stop is the whole formula; everything else is charges eating the R. Charges here come from the brokerage comparison, and the tax side of an F&O year from the F&O turnover and tax calculator.
Computation on your own numbers; not a signal, not a recommendation of any instrument or direction. Sizes round down to whole shares or lots. Charges use Zerodha's published rates on NSE. The survival strip is a simulation with fixed win rate and R; real edges are not fixed, and slippage and gaps make stops imperfect. Index lot sizes per NSE circular effective 27 January 2026; stock lots change quarterly.
Why one percent
Losses compound against you: a 50% drawdown needs a 100% gain to recover. At 1% risk, twenty consecutive losses — rare but not impossible for a 45% system — cost 18% of the account. At 5% the same run costs 64%, from which most traders never return. The strip puts your own numbers to this.
The stop sets the size
Size = rupee risk ÷ distance to stop. A wider stop means fewer shares, not more risk; a tighter stop means more shares for the same rupees. Conviction does not enter the formula. If the size the stop allows feels too small, the account is too small for that trade, not the other way round.
Charges eat R
A 2 R target is not 2 R once brokerage, STT, exchange fees and GST come off both legs — on the default trade it is 1.78 R, and on a tight intraday scalp the gap is larger still. Options carry STT at 0.15% of premium on the sell side since April 2026, which matters at small premiums.
What the strip measures
Two thousand simulated accounts, each trading your win rate and R for your number of trades, with the same random luck at every risk level so only the sizing differs. Survival is the share that never fell to the ruin line; the median worst drawdown shows what the survivors still went through. A closed-form risk-of-ruin check is in the source for anyone who wants the formula.
Frequently asked questions
What is position sizing?+
Deciding how many shares or lots to trade so that if the stop is hit you lose a fixed, small fraction of your account. Size = (account × risk %) ÷ (entry − stop). It is the only part of a trade you fully control, and it is what keeps a run of losses from ending the account.
What percentage of my account should I risk per trade?+
One percent is the widely used ceiling for a reason: at 1%, twenty straight losses cost about 18% of the account; at 5%, the same run costs 64%. The survival strip shows this for your own win rate and R — with a genuine edge you survive almost anything at 1%, while at 5% even a good system has a meaningful chance of a 50% drawdown inside 100 trades.
How do I size an options trade?+
Use the premium as the price. If you buy at ₹180 with a mental stop at ₹120, the risk is ₹60 per unit, so risk-in-rupees ÷ 60 gives units, rounded down to whole lots (Bank Nifty is 30). If you would let the option expire worthless instead of stopping out, the whole premium is the risk per unit.
Does this work for MTF or leveraged positions?+
The size calculation does not care where the money comes from; leverage only changes how much of the position is yours. When the position value exceeds the account, the tool flags it and points to the MTF calculator, because funding cost then becomes part of the R you are giving up.
What is expectancy?+
Average rupees made per trade: (win rate × average win) − (loss rate × average loss). At 45% wins and 1.8 R it is 0.45 × 1.8 − 0.55 × 1 = +0.26 R per trade. Positive expectancy is what makes survival possible; position size decides whether you stay in the game long enough to collect it.
Is this a trading signal?+
No. Nothing here suggests an instrument, a direction, an entry or a target — you supply all of those. The calculator computes size, R after charges, and survival odds from your own numbers. It gives the same answer for any stock and any index.
Sources and references
- Index derivative lot sizes effective the January 2026 series: NSE circular, verified 4 September 2026. NSE revised index lot sizes from the January 2026 series (monthly contracts from 27 January 2026). Stock lot sizes are revised every quarter and vary by scrip, so they are entered manually.
- Brokerage and statutory charges per broker from the brokerage comparison, which cites each broker's published schedule and the Budget 2026 STT rates.
- Risk-of-ruin methodology: fixed-fraction betting on a log-equity random walk; the Monte Carlo is seeded so results are reproducible, and the closed-form approximation is in
src/lib/position-size.ts.
Disclaimer: Educational computation on numbers you supply. It does not recommend any security, direction, entry, stop or target, and it is not investment advice. Simulations assume a constant edge; real trading has slippage, gaps and changing conditions. Trading in equities and derivatives involves risk of loss.
Related: Brokerage charges compared · F&O turnover & tax · MTF explained