The Nominal Cycle Ladder: 80, 40, 20, 10 Days, Explained

Market rhythm does not spread across an infinite range of frequencies. It clusters on a small, named set of cycle lengths, each about half the one above it — 18 years, 9 years, 54 months, 18 months, 40 weeks, 20 weeks, then 80, 40, 20, 10, and 5 days. J.M. Hurst measured that set across decades of data in the 1960s and called it the nominal model. I call the trading end of it the ladder, and the 80-day rung is the workhorse.

This page covers what the ladder is, why each rung doubles, why the names don't match the measured averages, which rungs an active trader actually lives on, and where the ladder's tolerances sit — because it has tolerances, and pretending a good tool is a perfect one is how people get hurt by it.

What exactly is the nominal model?

Hurst was an aerospace engineer, and he was the first analyst to put early computers to work on market price data. What came out of that work is a specific claim: the cycle periods active in the market are not random. They cluster on a small set of specific lengths, each with its own measured average wavelength, stable enough across many years of data to deserve names. That is Hurst's principle of nominality — the cycles can be named, and once named, they can be tracked.

Here is the model, with the average measured wavelength for each rung:

There are cycles above and below this table, but this is the working set. Everything longer than what you can see and phase on your chart gets summed into a single word — sigma-L, the sum of all longer cycles. Sigma-L is a cycle trader's precise name for trend, and it decides whether any given cycle on the ladder runs bullish, bearish, or neutral.

Why is each rung about half the one above it?

Hurst called it harmonicity: neighboring cycle periods relate by a small whole number, and that number is almost always two. Two 10-day cycles fit inside a 20. Two 20s inside a 40. Two 40s inside an 80. Two 80-day cycles inside a 20-week cycle, and on up the ladder. The classic model carries one factor-of-three step near the top of the range: three 80-week cycles combine into the 54-month cycle. Everything else doubles.

The companion principle is summation: the waves combine by simple addition. Price at any moment is the sum of every rung plus the trend beneath them, the way a chord is the sum of the instruments playing it. When several rungs push in the same direction at once, you get the big clean moves. When they push against each other, you get chop. Neither one is mysterious once you can see the rungs separately.

Harmonicity also produces the single most useful fact on this page: because the rungs nest by two, every trough of a longer cycle is also a trough of every shorter cycle beneath it. Troughs stack. Peaks do not. That is why market bottoms tend to form as sharp, well-timed V's while tops come in rounded and staggered — a whole article's worth of consequence on its own: why bottoms form faster than tops.

Why don't the names match the measured averages?

An "80-day" cycle that averages 68.2 days looks sloppy until you understand what the names are for. The nominal model is a ruler, not a schedule. Real instruments drift around the nominal values — a given market, on a given date, has its own current cycle lengths, and part of the analyst's job is measuring that drift against the named ruler. The names stay fixed so the measurement means something.

Hurst covered the drift itself with his principle of variation: everything in the model is a strong tendency, not a law. The 80-day rung runs roughly 60 to 80 calendar days trough to trough in practice. And the drift is not just slop to be tolerated — it carries information. Cycles finishing short of their average have tended to run bullish; cycles stretching long have tended to run bearish. The ruler tells you the deviation, and the deviation tells you something about the tide.

Which rungs does an active trader actually use?

Four of them: the 80, 40, 20, and 10-day cycles. Their rhythm is short enough to follow the market closely and precisely, long enough to stay readable on a daily chart. Here is how the four divide the work:

1. The 80-day cycle is the frame. About five of them arrive per year, and each one structures two to three months of price into one repeating shape. It gets my full write-up here: what is the 80-day cycle.
2. The 40-day cycles split the 80 into halves — the two legs of its "M" shape. The second 40 turns prices up midway through the 80 and, in bullish cycles, carries them to a higher peak.
3. The 20-day cycles set the trading rhythm. Four of them per 80, and the 20-day FLD divides the 80-day cycle into eight lettered times of interest, A through H.
4. The 10-day cycles are the finest rung I track. Eight per 80 — the small print inside each 20-day move.

One rung above the working set, the 20-week cycle still matters even if you never phase it: its trough lands on the same day as an 80-day trough, and the move out of a 20-week low is generally faster, cleaner, and longer-running than an ordinary one, because more rungs are pushing off the same floor at once.

How do the rungs interact on a chart?

Three principles govern how the ladder shows up on an actual daily chart:

• Synchronicity. The rungs phase themselves so their troughs coincide. A prominent low on the chart is prominent precisely because several cycles bottomed there together — which is why phasing analysis marks troughs with stacked diamonds, one row per rung.
• Proportionality. Amplitude scales with period. A longer rung moves price further than a shorter one, so the size of a swing hints at which rung produced it.
• Translation. The trend drags a cycle's visible peak off-center inside its span — peaks shift right in uptrends and left in downtrends. Which way a cycle's peak leans is one of the cleanest tells about the larger tide: left vs right translation.

All of the bookkeeping runs on troughs, not peaks, because troughs are the sharp, datable events. Finding them correctly is its own skill: how to identify a cycle low.

Where does the ladder show up in a scored record?

Every call I make on air gets logged the day it is made and scored later against what price did. Here is one where the ladder's rhythm was right and my clock was still wrong — I keep these on purpose:

July 9, 2026 — S&P 500, weakness expected into a downward FLD interaction — MISS. On the show I said the S&P had been weak going into a downward interaction of the 20-day rhythm, and that our bearish scans would "turn completely red" over the following several sessions — I named the window out loud, running from the next day through the following Wednesday. What happened: that window closed green. The rollover did come, but one to two sessions after the window I gave. Right idea, early on timing. Scored a miss.

That is the principle of variation charging its toll. The rungs give you windows, not appointments, and a stated window that misses by two sessions is still a miss — the ledger doesn't grade on intent. The full scoring rules live on the methodology page.

What is the ladder not?

The honest limits:

• It is not a metronome. Every rung's number is an average with a real spread around it. The 80-day rung alone ranges roughly 60 to 80 days. Anyone selling you cycle precision to the day is selling you something else.
• It is not universal in its particulars. The deep structure is shared across markets, but each instrument drifts. The nominal model is the ruler; the instrument's current cycle lengths are the measurement, and the measurement has to be redone as the chart grows.
• It is not a size forecast. Proportionality is a tendency, and news can inflate or deflate any single move without touching the timing structure.
• It is not self-executing. Placing the troughs — the phasing — is a judgment skill, not a mechanical procedure. The one directional rule that helps: work from the longest rungs down, because a longer cycle's troughs locate the shorter cycles' troughs beneath them, and never the reverse.

Questions traders ask

Where do the numbers 80, 40, 20, 10 come from?

From measurement, not theory. Hurst ran decades of price data through early computers and found the active cycle periods clustering around specific lengths. The round numbers are naming conventions; the measured averages behind them are 68.2, 34.1, 17, and 8.5 calendar days respectively.

Is the 18-month cycle the same thing as the 80-week cycle?

Effectively, yes. The 18-month rung measures about 17.9 months, which is roughly 78 weeks — and two 40-week cycles average 77.8 weeks. Same rung, two names, depending on which analyst's table you are reading. The ladder's structure doesn't change; only the label does.

Do individual stocks follow the same ladder as the index?

Broadly, yes — that is Hurst's principle of commonality. The financial markets are highly correlated, and stocks tend to share the dates where they pivot and bottom, which is why one good index chart reads for nearly all of them. Each individual name still drifts around the nominal values in its own way, so the index gives you the frame and the specific chart gives you the fine print.

What is sigma-L?

The sum of all cycles longer than what your chart can show — the multi-year tide underneath everything on the ladder. You cannot phase it directly; you infer it from how the visible cycles behave. It is what makes one 80-day cycle bullish and the next one bearish, and it is the cycle trader's exact word for what everyone else just calls trend.

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