The Best Time of Day to Buy Stocks, Measured

The honest answer to "what is the best time of day to buy stocks" is that it depends what you are trying to do, and that most of the advice you will read gets the shape of the day wrong.

So we measured it. Across 60 liquid US stocks and ETFs and roughly six and a half years of one-minute bars, here is how much a typical stock actually moves in each half hour of the session, and how much of the day's volume trades in it.

The first thirty minutes is not the same market as the rest of the day

Between 09:30 and 10:00 the average stock in our sample moved 32.7 basis points per minute, about a third of a percent every sixty seconds. By 13:30 that had fallen to 10.1. The opening half hour is 3.2 times as volatile as the quietest one, and it carries 16.2% of the entire day's volume in 8% of its minutes.

This is not a small effect at the edges. It means the same strategy, with the same rules, is being applied to two different instruments depending on when you run it. A ten-cent stop is noise at 09:35 and a considered risk decision at 13:35.

It also explains why the open attracts day traders and destroys new ones. The movement is genuinely there, which is the appeal. So is the spread, the incomplete information, and the fact that the price you see is frequently not the price you get. Opportunity and cost arrive together and beginners tend to notice only the first.

Volatility decays all day. Volume does not.

Look at the two series again, because they separate in the afternoon.

Range falls monotonically from the open until about 13:30 and then essentially flattens. Volume falls too, but then turns and produces a second peak into the close: the final half hour carries 13.7% of the day's volume, almost as much as the opening half hour.

Yet that closing half hour is only 1.26 times as volatile as the quietest period. Enormous volume, ordinary movement.

That combination is not a contradiction, it is what an auction looks like. Index funds, closing crosses, rebalancing and end-of-day hedging generate a great deal of size that is not trying to express a directional opinion. Both sides are heavy, so prints are large and prices do not travel far.

The practical consequence is that "trade the open or the close" is advice which bundles two entirely different sessions. If you are trying to capture movement, the open and the close are not substitutes. If you are trying to get a large order filled without pushing the price, the close is the best part of the day and the open is the worst.

The lunch hour is real

The middle of the session, roughly 12:00 to 14:00, is the deadest stretch by both measures. Range bottoms at 13:30 and volume bottoms right alongside it, at just under 5% per half hour.

For a breakout trader this is the worst part of the day, and not only because there is less movement. Thin conditions produce more failed breaks: a level gets tagged, there is not enough participation behind it to continue, and price falls back through. You get the trigger without the follow-through, which is the specific way that a strategy with a real edge still loses money.

For a mean-reversion trader the same conditions are the most favourable of the day, for exactly the same reason.

So what time should you actually buy?

Three honest answers, depending on who is asking.

If you are investing rather than trading, the time of day is close to irrelevant. A few basis points of intraday noise does not survive a holding period measured in years. If you want to reduce the chance of a bad print, avoid the first fifteen minutes and use a limit order. That is the entire optimisation available to you, and it is worth roughly nothing, which is the correct amount of attention to give it.

If you are day trading, trade when your method's conditions exist. A momentum method needs participation and has most of its opportunity before 11:00. A fade or reversion method is better served by the middle of the day. Running a breakout system at 13:00 because that is when you happen to be free is a real and common way to lose money slowly.

If you are placing a large order, the closing half hour is where the liquidity is. That is what all that non-directional volume is for.

What the averages hide

Every number above is a mean across 60 symbols and six and a half years, and a mean is a poor description of any individual morning.

A stock with news does not follow this curve. Neither does the whole market on an inflation print or a Fed decision, which can make 14:00 the most volatile half hour of the month. The curve describes the ordinary day, and the days that matter most to a trader are the ones that are not ordinary.

Use it as a baseline for what normal looks like, so you can recognise a session that is not normal. That recognition is worth considerably more than the schedule itself, and it is the part that takes time to learn. If you want to see it done out loud on a live session, you can sit in with our desk for three trading days.