What is a turnover budget in systematic trading?

A turnover budget puts an explicit ceiling on how much a strategy is allowed to trade over a given window. Instead of asking only whether the signal improves expected return, it also asks whether the amount of trading needed to express that signal is still economically sensible.

That budget can be measured in annualized turnover, expected notional traded, fee spend, or some other friction-aware metric. The important part is that it turns cost discipline into a design constraint rather than an after-the-fact apology.

Turnover budgets keep research honest when a strategy looks better mostly because it trades more. They are especially useful when several sleeves compete for capital and one fast strategy can quietly consume all of the operational room.

Once a turnover budget exists, threshold design, rebalance cadence, and even portfolio weights start to look different. A signal that barely improves expected return may not deserve a trade if it consumes too much of the budget, while a slower sleeve may earn a larger allocation because it spends less trading capacity.

A turnover budget should not be a blunt excuse to undertrade every fast idea. The goal is not to make the portfolio look quiet. The goal is to make the trading cost story explicit enough that you can tell the difference between real edge and edge borrowed from unrealistic execution.