Position Size Calculator for Stock Traders
Never risk more capital than planned. Calculate the exact number of shares to buy or short based on your defined risk percentage and stop-loss level.
The Mathematics of Position Sizing
Professional risk management dictates that you should determine your trade quantity from your risk budget, rather than picking an arbitrary round number of shares.
Position Size Formula:
By enforcing this rule, a losing trade will never damage your account beyond your pre-set risk parameter (typically 1% to 2% per trade).
Example: with a ₹1,00,000 account and 1% risk, you can lose ₹1,000 on the trade. Buying at ₹2,500 with a stop-loss at ₹2,460 risks ₹40 per share, so the right size is 1,000 ÷ 40 = 25 shares (₹62,500 of capital). With a tighter stop at ₹2,480 the risk is ₹20 per share and the size becomes 50 shares, but the loss if the stop is hit is still ₹1,000.
- 1Capital ₹1,00,000
- 2Risk 1% = ₹1,000
- 3Stop distance ₹40
- 4₹1,000 ÷ ₹40 = 25 shares
Position Size for Futures and Options (Lots)
In F&O you trade whole lots, so work out the risk of one lot first: risk per lot = lot size × distance to the stop-loss. The number of lots is your risk budget divided by that, rounded down.
Example: RELIANCE futures trade in lots of 500 shares. With a stop-loss ₹4 away, one lot risks 500 × 4 = ₹2,000. A ₹5,000 risk budget allows 2 lots (₹4,000 at risk). If a single lot risks more than your whole budget, the correct size is zero: skip the trade or choose a smaller instrument.
| Contract | Lot size | Risk per lot with a 10-point stop |
|---|---|---|
| NIFTY | 65 | ₹650 |
| BANKNIFTY | 30 | ₹300 |
| RELIANCE | 500 | ₹5,000 |
| HDFCBANK | 650 | ₹6,500 |
| SBIN | 750 | ₹7,500 |
Lot sizes from NSE's published market-lots file (September 2026 contracts). NSE revises lot sizes from time to time, so check the current lot before trading.
Frequently Asked Questions
How much should I risk per trade?
A common rule of thumb is 1% to 2% of the account on any one trade. At 1%, ten losing trades in a row cost about 10% of the account, which leaves room to recover.
Where should I put the stop-loss?
At the price where your trade idea is proven wrong, such as below the support level or the day's low. Choose the stop first and let the formula decide the quantity; never move the stop just to fit a bigger quantity.
What if the capital needed is more than my account?
If capital use shows more than 100%, you cannot buy the full quantity with your own money. Buy what your capital allows; your risk on the trade will then be smaller than the budget.
Does this include brokerage and taxes?
No. The risk budget covers the price move only. Brokerage, STT and other charges add a little to the loss on every trade; the brokerage calculator shows how much.
How do I size a futures or options trade?
Multiply the lot size by the distance to your stop-loss to get the risk of one lot, then divide your risk budget by it and round down. If one lot already risks more than your budget, skip the trade.
How wide should the stop be? See how 0.5% to 2%, ATR and trailing stops tested on NSE.