Compounding vs Fixed Position Sizing: Which Should You Deploy?

Two deployments can run the identical strategy, take the identical signals on the identical pair, and still end the year far apart. The difference is often not the strategy at all. It is how each trade was sized.

The two modes in one line

• Fixed cash, every trade uses the same rupee or dollar amount, regardless of how the account has performed
• Compounding, every trade uses a percentage of your CURRENT equity, so it grows after wins and shrinks after losses

Why the difference compounds, literally

Imagine $100 of starting capital and a fixed $10 per trade. If the account grows to $200, you are still risking $10, which is now only 5% of equity. The strategy is quietly getting more conservative exactly as it proves itself.

Percentage sizing does the opposite. At 50% of equity, $100 puts $50 to work. After a win takes you to $110, the next trade uses $55. After a loss takes you to $95, it uses $47.50. The position tracks the account instead of ignoring it.

Compounding magnifies both wins and losses, but asymmetrically: losing streaks auto-shrink the position size, while winning streaks auto-expand it.

The trade-off nobody mentions

A steeper equity curve comes with a deeper drawdown. A losing streak under percentage sizing happens at a larger position size than the same streak under fixed sizing, so the peak-to-trough dip is bigger in both percent and absolute terms.

When a strategy locks the sizing for you

Some strategies ship with position sizing locked. That is deliberate: the published backtest was produced at that specific sizing, and letting the number be dialled somewhere else would make the report on the page a description of something you are not running. When the deploy dialog greys the field out, it is protecting the link between what you read and what you deploy.

Which should you pick?

• Choose fixed cash when you are testing a new strategy, when your capital is close to the broker minimum, or when a predictable per-trade risk helps you sleep
• Choose compounding when you have already watched the strategy run, you accept the deeper drawdowns, and you intend to leave it alone for six to twelve months

Fixed cash is the safer starting point. Compounding is for capital you have decided not to touch, running a strategy you have already seen behave. If you are unsure which describes you, that uncertainty is itself the answer.