Position size calculator
Decide how many shares to buy based on what you’re actually willing to lose — not on a round number that felt right.
How position sizing works
The idea is to flip the usual question. Instead of "how many shares can I afford," you ask "how much am I willing to lose if I’m wrong" — and let that decide the size. Most disciplined traders risk a small, fixed slice of their account per trade, often 1–2%.
The math is straightforward. Your risk amount is your account size times your risk percentage. Your risk per share is the distance from your entry to your stop-loss. Divide one by the other and you get the number of shares that keeps your loss capped at what you decided in advance:
shares = (account × risk%) ÷ (entry − stop)
The point of doing it this way is that a wide stop forces a smaller position and a tight stop allows a larger one — so a single loss costs you the same either way. Your downside stops being a surprise.
Educational tool, not financial advice. Your figures never leave the page — the calculation runs entirely in your browser. The page loads standard pageview analytics, which never sees your numbers.
This math stops at what you typed in.
Tradune runs it continuously on your real holdings — with your money-weighted return next to a buy-and-hold SPY twin, and SEC insider filings flagged on the stocks you own.
Educational analytics — not investment advice.