How to Use the ATR Position Size Calculator

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What this calculator actually helps you understand

The ATR Position Size calculator exists for investors who want to tie size to volatility via atr stops. It turns that decision into a repeatable checklist instead of a guess. It works best when historical atr represents forward volatility. Rather than promising outperformance, it helps you surface the trade-offs described as “Demonstrate volatility regime adjustments.”

Inputs explained (with realistic examples)

Account size or risk capital: How much capital you are willing to size from. Use current equity, not a rounded number from memory.
Risk per trade: Either a fixed cash amount or a percentage of equity that you can afford to lose if the stop is hit.
Entry and stop levels: Your planned fill price and the level where you will exit if wrong. Both should factor in slippage and volatility.

Outputs: how to read the results

Recommended position size: How many units you can hold while respecting the risk cap.
Cash at risk: The loss you accept if the stop executes as planned.
What it does not do: Guarantee returns or outcomes. It simply applies the assumption "Historical ATR represents forward volatility" to your inputs.

Common mistakes people make

Mixing timeframes (daily ATR for intraday).
Treating the output as a forecast instead of a scenario.
Ignoring fees, taxes, or behavior changes that sit outside the model.

When this calculator is genuinely useful

When you need a calm way to tie size to volatility via atr stops without hand-waving.
When you want to communicate the rationale behind atr position size decisions to a partner, advisor, or investment committee.
When you need to compare multiple scenarios quickly (best/middle/worst).

When this calculator can mislead you

When the core assumption (“Historical ATR represents forward volatility”) clearly does not hold in your situation.
When inputs are based on optimistic guesses rather than verifiable numbers.
When behavioral factors (sticking with contributions, honoring stops, etc.) matter more than the math.

How this fits into a broader financial decision

ATR Position Size is one slice of the decision. Pair it with qualitative checks: liquidity needs, tax context, counterparties, and diversification. Link it with companion calculators (for example: Demonstrate volatility regime adjustments) so readers see how today’s choice affects the rest of the plan.

Use the calculator

👉 Try the calculator here

Rules

Do not treat any scenario as personalized advice.
Stay conservative with inputs and double-check assumptions before acting.
Avoid country-specific tax or regulatory claims unless you verify them yourself.

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