Live 12-month momentum — S&P 500 (SPY)
+24.9% (12-mo, ex last month)
Positive trend
As of 2026-06-12 · educational, not investment advice
See this alongside every signal on the market dashboard →What it is
Momentum is the simple idea that a market’s recent direction tends to continue. Concretely, it is the total return over roughly the past year: if the market is up over the last twelve months, it has positive momentum; if it is down, negative. Unlike RSI — which measures short-term, days-to-weeks stretch — this is a slow, months-long trend factor, and it is the one with serious academic weight behind it.
The effect was formalised in the 1990s and has since been found across nearly every market and asset class studied, going back over a century. That persistence is why momentum is treated as a genuine "factor" alongside value and size, rather than a chart-reading folk belief. It is one of the four reasons people watch timing signals at all: not to predict, but to lean with a tendency that has actually shown up in the data.
A common refinement, and the one used in the live reading here, is to measure the past year but skip the most recent month — the "12-minus-1" momentum. The reason is that over very short horizons prices tend to do the opposite and snap back, so dropping the last month removes that short-term reversal noise and leaves the cleaner medium-term trend.
How it's calculated
You take the price about twelve months ago, compare it with the price about one month ago, and express the change as a percentage. Roughly: (price one month ago ÷ price twelve months ago) − 1. A positive number means the market climbed over that window; a negative one means it fell. The live figure on this page runs exactly that calculation on the S&P 500.
Skipping the most recent month is deliberate. Over a few weeks, prices have a mild tendency to reverse rather than continue, so including the very latest move would add noise that works against the signal. Stepping back one month sidesteps that short-term reversal and isolates the medium-term trend that momentum is actually trying to capture. There is no thresholds-and-bands machinery here — momentum is essentially a direction and a magnitude.
How to read it
Strongly positive — clear uptrend
Bullish leanThe market is meaningfully higher than a year ago. On the historical record this tendency has persisted more often than not — the single most reliable thing about momentum. Strength tends to beget strength, for a while.
Around zero — flat / transitional
NeutralThe past-year return is close to flat. Momentum carries little information here; the market has no clear medium-term direction, and this is exactly the kind of environment where it can flip sign without warning.
Negative — downtrend
Bearish leanThe market is lower than a year ago. Negative momentum has, on average, tended to persist too — but downtrends are where momentum’s sudden, violent reversals also live, so the signal is at its least comfortable here.
When it fails
Momentum’s failure mode is the "momentum crash". The strategy works smoothly for long stretches and then, at major turning points — the bottom of a bear market especially — it reverses with shocking speed. The exact moment a beaten-down market rips higher off a low, a rule that was leaning short or sitting out gets hit hardest, giving back months of gains in days. The edge is real on average; it is just not smooth, and the worst losses are concentrated and sudden.
The other limit is horizon. Momentum is a months-long signal, so on any given day or week it says almost nothing — reacting to it like a short-term trigger is a mistake. It is also two-sided in a way that feels unnatural: it tells you to lean with a falling market as well as a rising one, which is the opposite of "buy low". The honest use is as one slow input among several — a tendency to respect over months, never a precise in-or-out call for tomorrow.
See it for yourself
Build a systematic model
Put momentum to work inside a simple rules-based model, combine it with a trend filter, and watch how it behaves across a full cycle — the long smooth edge, and the sharp reversal at the turn.
Build a systematic model →Frequently asked
- What is momentum in the stock market?
- Momentum is the tendency of a market or stock that has performed well over the recent past — typically the last year — to keep performing well for a while, and vice versa for poor performers. It is measured as the total return over a trailing window, usually twelve months. It is one of the most robustly documented effects in finance, found across many markets and over long history.
- How is 12-month momentum different from RSI?
- They operate on completely different clocks. RSI is a short-term oscillator measuring how stretched a move is over days to weeks, and it is mean-reverting — extremes are expected to snap back. Twelve-month momentum is a slow, months-long trend factor that bets the recent direction continues. RSI says "this has run too far, too fast"; momentum says "this has been going up for a year and tends to keep going". They can easily point in opposite directions.
- Why skip the most recent month in 12-month momentum?
- Because over very short horizons — the last few weeks — prices tend to reverse rather than continue, the opposite of the medium-term momentum effect. Including that most recent month would add short-term reversal noise that works against the signal. Measuring the year but dropping the latest month (the "12-minus-1" approach) isolates the cleaner medium-term trend. It is a standard refinement used in academic momentum research.
- Does momentum work for timing the market?
- On average and over months, momentum has a genuine, well-documented edge — but it is not smooth and not a short-term tool. Its worst losses come in sudden "momentum crashes" at major turning points, especially off bear-market lows, where it reverses violently. It is best used as one slow trend input combined with other signals, and respected over a multi-month horizon rather than acted on as a same-day buy or sell trigger.
Keep going
- RSI — overbought & oversold →
- The 200-day average →
- Where the market sits today →
- See what mistiming the market actually costs →
Educational, not investment advice. No signal predicts the future, and no single reading is a buy or sell instruction — this is a structured way to understand what each timing signal is actually telling you.