Most stock screeners skip the part that matters most

Here's a scenario most traders know well. You read about a setup, build a screen for it, and it returns 30 stocks. Some of them look great on the chart. You pick a few, put on positions, and... it's a coin flip. Some work, some don't, and there's no way to tell whether the screen itself is any good or the results were just random.

The problem isn't the screen. The problem is that the most important step was skipped: checking whether this pattern had any edge in the first place.

The gap in most screeners

Finviz, TradingView, Yahoo Finance, and most broker-provided screeners all do the same thing. You pick some filters, hit search, and get a list of stocks that match right now. That's useful, but it only answers half the question.

The other half: “when stocks matched these exact filters in the past, what happened next?” Almost no screener answers that. You're left doing it manually (which nobody actually does systematically) or just assuming that a pattern works because it looks right on a few examples.

What a backtest needs to be useful

A backtest that just reports the average return is barely better than nothing. If the average forward return is +3%, that sounds good until you realise half the signals lost 10% and a few massive winners pulled the average up. The average hides the thing you most need to see: the distribution.

That's why Breakout Scanner shows win rate, average, median, and P10/P90 for each screener configuration that gets backtested. The median tells you what the typical outcome was. The P10 tells you how bad the bad ones got. The gap between the average and the median tells you whether the edge comes from a few outliers or from something more consistent.

Time horizon changes everything

A breakout screen might have a great win rate over 20 days and a terrible one over 5 days. Or the reverse. The holding period you plan to use should match the horizon you test against. This sounds obvious, but when a screener doesn't offer backtesting at all, you can't even check.

Breakout Scanner shows results across multiple horizons (5-day, 10-day, 20-day, 60-day) side by side, making it possible to identify where a pattern has an edge and where it doesn't. Sometimes a setup is strong as a two-week hold but gives back everything by month-end. That's important to know before trading it.

The honest limits of backtesting

It's worth being direct about what backtests can't do. They assume every signal would have been taken, which in practice never happens. They don't account for slippage on entry or exit. They don't know about the news event that would have kept you out of a trade. Survivorship bias is real: you're testing against stocks that still exist, not the ones that delisted.

Backtests are useful for ruling out bad ideas quickly and for understanding the rough shape of a strategy's past results. They are not a guarantee of future performance. Breakout Scanner is explicit about these limitations because traders deserve honest tools, not overconfident sales pitches.

The workflow that helps

A productive approach: come up with an idea for a screen. Build it (in Breakout Scanner, by typing it in plain English). Backtest it before trading it. Look at the distribution of outcomes, not just the average. If the numbers are interesting, run the screen live and start watching the signals it produces. If the numbers aren't there, discard it and try something else.

This loop (idea, screen, test, evaluate) is what most traders do in their heads already. The backtest lab just makes it faster and puts real numbers behind the “would this have worked?” question.