Every position-sizing mistake starts the same way: picking the size first and checking the risk after.
Account size, risk per trade, entry, stop.
Four numbers. That is the calculation. Most traders still do it in their head, on a napkin, or not at all.
And the math is not hard. It is easy to skip when the setup looks good and the order's already half-placed in your head.
Type your account size, your risk percentage, your entry, and your stop into four cells. The sheet returns your dollar risk, your position size, your position value, and the percent of your account that trade would deploy.
Then it does something a napkin cannot: it shows you the same entry and stop across eight different risk percentages, side by side, so you can see the full range before picking one.
Position size always rounds down. The dollar amount at risk never creeps past your target because of a fractional share or contract.
One tab, four inputs. It works for stocks, ETFs, futures, or forex.
A Trading Habits Tool
The Position Size Calculator
Risk-based position sizing across a full range of risk percentages, at once.
- Format Excel workbook (.xlsx), opens in Excel, Google Sheets, or Numbers
- Tabs Calculator, Instructions
- Inputs Account size, risk per trade, entry price, stop price
- Delivery Instant download right after checkout
Four numbers in. Every result you need out.
What's Inside
What's Inside The Position Size Calculator
- 01Four inputs: account size, risk per trade, entry price, stop price. Change any one and every result recalculates immediately.
- 02Position size always rounds down to the nearest whole share, unit, or contract, so the dollar amount actually at risk never exceeds your target.
- 03A built-in Risk Comparison table showing your exact entry and stop at eight risk percentages, from 0.25% up to 3.00%, without re-entering a single number.
- 04Works for stocks, ETFs, futures, or forex, anything priced in dollars per share, unit, or point.
- 05Yellow-highlighted input cells, so it's always obvious which four numbers actually drive the sheet.
- 06Percent of account deployed calculated automatically, right alongside your dollar risk and position size.
- 07An Instructions tab that walks through exactly how each formula works, in plain language, not spreadsheet jargon.
- 08No macros, no add-ons, no subscription. One tab. Opens in Excel, Google Sheets, or Numbers.
HABITS
★
Certificate of Guarantee
60-Day, No-Questions-Asked
If The Position Size Calculator doesn't earn its place on your desk, email us any time within 60 days of purchase for a full refund. No form to fill out. No reason required.
Instant Download
$9One-time payment. No subscription.
Order NowXLSX WORKBOOK · DELIVERED IMMEDIATELY AFTER CHECKOUT · 60-DAY GUARANTEE
Behind The Tool
Where Risk-Based Position Sizing Came From
The Concept
Risk-based position sizing starts from a different question than most traders ask first. Instead of "how many shares can I afford," it asks "how many shares can I afford to be wrong on." Account size, entry, and stop already answer that question mathematically. The only number left to choose on purpose is the percentage of the account willing to be risked on any single trade.
That one decision, made in advance and applied consistently, is what keeps a string of losing trades a setback instead of an account-ending event.
Where It Comes From
The math traces back to Bell Labs scientist John L. Kelly Jr., whose 1956 paper "A New Interpretation of Information Rate" solved a problem in signal transmission that turned out to double as a formula for optimal bet sizing. Mathematician and hedge-fund manager Edward O. Thorp carried the idea into blackjack in Beat the Dealer (1962), then into financial markets.
Trader and author Ralph Vince formalized fractional position sizing for retail traders in Portfolio Management Formulas (1990), and it's since become standard practice under a simpler name: risking a fixed percentage of account equity per trade, exactly what this calculator solves for.
Why The Risk Percentage Matters More Than It Looks
Account remaining after 10 straight losing trades, each sized at a fixed percentage of remaining equity: (1 − risk%)10. A jump from 1% to 5% risk per trade doesn't quadruple the drawdown, it more than quadruples it, because every loss shrinks the base the next one is calculated against.
Try It: Live Position Size
This runs the same math the full workbook runs: four inputs, three outputs, live in your browser right now. The download version adds a saved risk-comparison table, per-trade caps, and a version that runs across an entire watchlist instead of one symbol at a time.
Common Questions
Why does 5% risk per trade lose more than five times what 1% loses?
Compounding against a shrinking base. Each loss reduces the equity the next trade's risk is calculated from, so the drawdown formula is (1 minus risk%) to the power of the number of losing trades, not simple multiplication. The chart above shows the real gap: 1% risk loses 9.6% of the account after ten straight losers, 5% risk loses 40.1%, more than four times worse, not five times, but still far past what a naive multiplication would predict.
Is 1% risk per trade a hard rule?
No single number is universal here. It's a common starting point because the math in the chart above shows how fast the drawdown accelerates past it, not because 1% is magic.
Does this calculator account for slippage or commissions?
No. It solves the same four-input math the full workbook runs: account size, risk percent, entry, and stop, nothing more. The downloadable version adds a saved comparison table and a per-trade cap across an entire watchlist.
Who actually formalized this for retail traders?
Ralph Vince, in his 1990 book Portfolio Management Formulas, building on the Kelly Criterion math Ed Thorp had already carried from Bell Labs into blackjack decades earlier.