Position sizing: why what you buy is only half the decision

You have researched a company and decided to invest. The next question sounds simple: how much?

This is position sizing: deciding how much capital a holding receives, and how that allocation can change over time.

Conviction needs a boundary

It is natural to invest more in an idea you feel strongly about. But confidence in a company does not remove uncertainty about its future.

Consider a simplified example. If a holding represents 5% of a portfolio and its price falls by 20%, its direct contribution to the portfolio's decline is approximately one percentage point. At a 25% allocation, the same price fall contributes approximately five percentage points.

This illustration assumes everything else remains unchanged and excludes costs. The stock's performance is identical; the allocation changes its impact.

Equal amounts do not mean equal risk

Dividing capital equally can be straightforward. It does not make every holding equally risky.

Two stocks with the same allocation may differ in how sharply their prices move, how easily they can be traded and how they respond to changing market conditions. Holdings can also share risks, so examining each position separately may miss their combined exposure.

A sizing method may consider these differences alongside position limits and other constraints. However, historical estimates remain estimates. They cannot establish exactly how a holding will behave next.

Position sizes change even when you do nothing

Suppose an illustrative ₹1,00,000 portfolio is divided equally across ten stocks. Each starts with ₹10,000, or 10% of the portfolio.

One stock doubles while the other nine remain unchanged. That holding is now worth ₹20,000 within a ₹1,10,000 portfolio - approximately 18.2%.

Limits involve choices

A position limit can establish how a strategy responds when a holding becomes too large. Depending on the rules, it might restrict further purchases, trigger a reduction or allow a temporary deviation.

Reducing a position can lower concentration, but it can also reduce participation if that holding continues to rise. Rebalancing creates transactions, which can introduce costs and tax consequences.

Practical constraints matter too. Whole-share quantities, minimum order values and available capital can prevent a portfolio from matching intended allocations precisely.

What should you ask about a strategy's sizing?

• What determines the initial allocation? Understand whether sizing follows equal weights, model outputs, risk estimates or another disclosed method.
• What can change it? Price movements, new signals and portfolio constraints may affect allocations differently.
• What happens at a limit? Check how the strategy handles an oversized position rather than assuming it sells immediately.
• What can prevent the intended allocation? Consider capital requirements, trading restrictions and execution differences.

Where information is missing, seek clarification rather than inferring the rules from a risk label or a return chart.

Understand how much each decision matters

When evaluating Fundgazer's algorithm-driven portfolios, consider the allocations alongside the eligible assets, simulated trades and available strategy information.

Explore our portfolios to review their approach, allocations and risk information.