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RSI period on M1: what changes between 7, 14 and 21 beyond speed

Most discussions of RSI period end with shorter is faster, longer is smoother. That's true, but there's more to it for M1 scalping.

With a short period like 7, RSI hits overbought and oversold readings much more often. On M1 that can mean dozens of readings above 70 or below 30 in a single session. If you use those levels as signals, you'll get a lot of them, and most will be noise. The levels themselves start to lose meaning, and some people move them to 80 and 20 to compensate.

With 14, the default, readings at the extremes are less frequent, and on M1 they often line up with short bursts of momentum rather than true exhaustion.

With 21 or longer, RSI moves slowly enough that it starts behaving more like a trend gauge. It might sit above 50 for long stretches in a trending session, and the extremes become rare.

So the choice of period changes what the indicator is measuring, not just how fast it reacts. A short period is closer to a measure of the last few candles' momentum. A longer one is closer to a measure of the session's direction.

The useful question is what you want it to tell you, and then picking a period and levels that fit, rather than tweaking until a backtest looks good.

One thing to keep in mind is that changing the period and keeping the same 70 and 30 levels isn't a fair comparison. A short period RSI naturally swings further, so the same levels produce more signals. If you want to compare periods honestly, it helps to adjust the levels so each version produces a similar number of signals, then see which ones line up better with what you care about. Otherwise you're mostly comparing signal frequency rather than signal quality, which isn't the same question. Matching signal counts first and then comparing is a fairer test.

Also worth checking whether your platform calculates RSI the same way as another one you use. Most use Wilder's smoothing, but some tools offer variations, and the first values after loading a chart can differ depending on how much history is used to seed the calculation. On M1 with limited history loaded, that can mean the RSI value on your screen doesn't quite match what someone else sees on theirs. Usually small, but it can matter if your rules depend on an exact level being crossed. Loading more history on the chart usually settles the values down.