Stock Position Sizing Calculator: a practical guide
How many shares fit my cash and planned-loss limit?
Work out how many whole shares fit your cash and chosen loss limit.
By VolatileShares · Example version 1 · Updated . Hypothetical inputs, not financial recommendations or live company data.
A worked example, in plain English
The idea in 10 seconds: Two limits matter: cash to buy the shares and money you could lose at your stop.
Which limit is doing the limiting?
The planned loss is not a guaranteed maximum. Gaps and fees can cost more.
- Whole shares
- 10
- Position cost
- $200.00
- Risk budget
- $20.00
Walk me through the full calculation
You chose to risk 1% of $2,000.00 in available cash, setting a $20.00 risk budget. 10 whole shares at $20.00 would cost $200.00, with a planned stop loss of $20.00. That planned stop loss is 1% of available cash. The chosen risk percentage is a ceiling, not the percentage you necessarily lose at the stop.
$1,800.00 of cash stays outside this position. The calculation rounds down and respects both entered budgets. It does not recommend a position, account for other holdings or guarantee a stop fill; actual losses can be larger.
The loss budget, rather than all available cash, is the tighter ceiling here.
Inputs used for this example
These are the calculator's example defaults, not suggested amounts or rates. Market calculators initially display USD. Change currency in the toolbar without creating a personal profile. Under optional Location & display settings, choose an example country for its currency and available historical CPI. Review any example household size and rent assumption before explicitly applying local assumptions: matching unedited budget/inflation fields change, while edited or restored inputs are kept. Lifestyle budgets are fictional examples, not measured national averages. Local tax, pension and borrowing links are guidance, not personal calculations. Switching currency alone does not change percentages, ages or share counts.
- Cash available for this example (USD)
- 2,000
- Cash you allow for the planned loss (%)
- 1
- Price you plan to buy at (USD)
- 20
- Stop price (USD)
- 18
Work backwards from your goal
How much cash would fit this many whole shares?
Start with a whole-share goal to find the cash it would need.
Choose Work backwards, enter your target and the few essential inputs, then choose Calculate my goal. The answer is checked with the same forward calculation and applied in one step. Example assumptions are disclosed under More options. Expand Calculation details & tools only if you want more detail. Impossible or out-of-range goals show an error instead of invented numbers. Long numbers display commas while editing; calculations and saved snapshots keep the original precision.
Return to the interactive calculator above →How the calculation works
Risk budget = account x risk % / 100. Shares = floor(min(risk budget / (entry - stop), account / entry)). Planned loss = shares x (entry - stop).
What this cannot tell you
Long, cash-only, whole-share scenario; not a recommended allocation. Excludes other holdings, fees, margin, liquidity and slippage. Actual losses can exceed the planned stop loss.
Changing an assumption changes the example, not the future. Verify source dates and actual product, tax and lending terms before relying on any result. These tools do not replace appropriately qualified advice.
There are two ceilings, not one
A $100 loss budget allows 50 whole shares at $2 of planned risk per share, but only 25 at $4, if cash is not the tighter limit. A large risk-budget percentage does not mean that same percentage is the planned stop loss. Cash and whole-share rounding can cap the position first.
Illustrative arithmetic, not market evidence or a promise of returns.
Keep a useful starting point
In the interactive calculator, compare different assumptions or explicitly save a named snapshot to My browser notebook. Saving is optional and browser-only, not an account or cloud backup. Revisit it on the same browser profile; restoring never refreshes prices or assumptions.