Flat Base
A flat base is a shallow, horizontal consolidation that forms after a stock has already advanced. Unlike a cup, it has no rounded shape. Price simply moves sideways in a narrow band, typically correcting far less than a standard base.
- Bias
- Bullish
- Category
- Chart Patterns
- Scan cadence
- Every close
What has to be true for a Flat Base to trigger
- A prior advance into the base
- A sideways range with a well-defined ceiling and floor
- A shallow correction, since flat bases are notably tighter than cups or double bottoms
- Enough duration to count as a base rather than a brief pause
- Volume quieting through the range
How PatternGrade grades it
Tighter and shallower ranges grade higher, as do bases that hold their floor cleanly rather than undercutting it repeatedly. Depth near the upper end of the acceptable range, or a ragged floor, lowers the grade.
Every scanner grades its hits A+, A or B from the pattern's own measurable structure. The grading is deterministic — the same chart always produces the same grade. It describes how closely the chart matches the pattern, not how likely anything is to happen; no hit rate or probability is attached to a grade. The reasoning is set out in the methodology.
What a Flat Base looks like in practice
After a 60% run over five months, a stock stops advancing and spends seven weeks between roughly $98 and $110, an 11% range with no trend inside it. Highs cluster near the top of the range, lows hold near the bottom, and volume settles to about two-thirds of what it was during the advance. Nothing dramatic happens for almost two months; that is the pattern.
How a Flat Base fails
A flat base fails by deepening. Once price cuts more than about 15% below the high the structure stops being flat and becomes a proper correction. The shallow-base argument is that holders are refusing to sell at any discount, and that argument no longer holds. The other failure is the false breakout: price pokes above the range on light volume, fails to follow through, and slides back inside. Bases that get undercut repeatedly tend to keep failing.
What this pattern is telling you
Flat bases often form after a prior base has already broken out, which means the stock may be further along in its advance and carrying more risk than the tight range suggests.
PatternGrade is not a financial advisor and does not give buy or sell recommendations. Targets and stops shown on a pattern are reference levels derived from its geometry, not advice.
How to scan for Flat Base setups
PatternGrade rescans every liquid US stock (~4,500 names) for this pattern after every close and returns the hits as a graded list, with the pattern drawn on each chart, so you review setups rather than hunt for them.
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Flat Base FAQ
What is a flat base in stocks?
A shallow, horizontal consolidation following an advance: a stock digesting gains in a narrow sideways band rather than a deeper, rounded correction.
How long does a flat base last?
Typically several weeks. Anything shorter is a pause rather than a base; PatternGrade requires enough duration for the range to qualify.
How shallow does a flat base have to be?
Conventionally under about 15% from high to low, and the tightest examples are under 10%. The shallowness is the entire signal: holders are not willing to part with stock even at a modest discount. A 25% range is a correction wearing a flat base's name.
How long should a flat base run?
Usually five to twelve weeks. Shorter than about five weeks and there has not been enough time for supply to change hands; much longer and the stock's momentum has generally decayed, which shows up in the grade through the trend component.
Is a flat base bullish?
It is a continuation structure, so it is read as bullish in the context of a prior advance. The same range appearing after a decline carries no such implication. PatternGrade weights the trend leading into the base for exactly this reason.
What makes a flat base grade A+?
A genuinely tight range, a strong advance into it, volume drying up as the base matures, and price holding in the upper half of the range rather than sagging toward the lows. A base that is technically within range width but spends its time near the bottom of it grades poorly.
Patterns a Flat Base is mistaken for
- Cup & Handle
- A cup is deeper and rounded, usually correcting 15-35%. A flat base is shallow and horizontal, typically under 15%. If the base has a visible curve, it is a cup.
- Darvas Box
- A Darvas box is defined by repeated rejections at a specific ceiling and floor. A flat base only needs a tight overall range. Every Darvas box is a flat base; not every flat base has the clean repeated tests that define a box.
- Base on Base
- A base on base is two consecutive bases where the second forms above the first without much net progress. If the current flat base sits directly on top of a prior one, that is the stronger read.
- Consolidation Breakout
- Consolidation breakout is the generic case and fires on the break itself. A flat base names the structure while it is still forming.
Last reviewed . Structure and grading for the Flat Base are reviewed against the scanner's own rules.