RSI (14) — Relative Strength Index
What it measures¶
The Relative Strength Index compares the size of a share's recent rises with the size of its recent falls, over 14 sessions, and scales the result from 0 to 100. Near 100, the recent sessions were almost all rises; near 0, almost all falls; around 50, a balance. J. Welles Wilder published it in 1978. Despite the name, it has nothing to do with relative strength against a benchmark — it compares the share only with itself.
Why it is on the page¶
It is the most widely used measure of how stretched a recent move is. On the Technical page it sits in the momentum panel; on the Price & timing strip it is shown beside the Momentum votes as a reading only — it never votes. A share in a strong, healthy rise often reads above 70 for weeks, so a high reading is not counted against it.
Thresholds, their source and the population they were fitted on¶
| Zone | RSI | Wilder's reading |
|---|---|---|
| under 30 | 0 to 30 | "oversold" — falls have dominated recently |
| 30 to 70 | 30 to 70 | neither stretched nor washed out |
| over 70 | 70 to 100 | "overbought" — rises have dominated recently |
The top zone is coloured amber, never red: in a rising trend, a high reading describes strength, not danger.
- Source: J. Welles Wilder, New Concepts in Technical Trading Systems (1978).
- Fitted on: no statistical sample — Wilder's convention. Independent tests found short-horizon RSI rules losing much of their edge after publication.
- Evidence grade: practitioner convention.
A worked example¶
On daily bars to 23 October 2026: Honeywell International read 66 and Apple 64 — both in the middle zone. As the Technical page showed it on 9 August 2026, Celestica read 47.64: momentum flat, neither stretched nor washed out.
What “No verdict” means here¶
RSI carries no verdict and no vote. The row reads insufficient data when fewer than 15 daily bars are stored. A reading from the stored indicator data and one computed from the bars on the page are labelled separately, so you always know where a figure came from.
What the verdict is and is not¶
The figure describes the balance of recent rises and falls. A reading above 70 is not a warning that the price will fall, and one below 30 is not a promise that it will rise — strong trends stay at either extreme for long stretches. It is not an instruction to trade the shares.