# Heads-Up Button Open Range: Sizing and Break-Even Fold Thresholds

> Heads-up button open range and size: break-even fold rates for 2x to 3.5x opens, big-blind defense, and why published numbers disagree. Worked examples.

- Source: https://toolsgambling.com/blog/heads-up-button-open-range
- Publisher: ToolsGambling
- Published: 2026-10-26
- Updated: 2026-10-26
- Cite as: "Heads-Up Button Open Range: Size and Fold Math", ToolsGambling, https://toolsgambling.com/blog/heads-up-button-open-range

A heads-up button open is the first preflop raise made by the player who holds the button and the small blind at once, so acts first before the flop. At 2.5 bb, a no-equity open reaches the threshold against folding at **57.1%** BB folds. Folding costs −0.5 bb because the small blind is already posted. The 71.4% figure is break-even against zero, not against folding; the gap is 14.3 percentage points. Open wider than at a six-max table: the authors’ starting point is **70–85% of combinations**, with the range and size adjusted to how often the BB folds. An effective stack of 100 bb is our assumption; the sources do not state depth. The calculation excludes postflop play and rake.

## What a heads-up button open is

At a two-player table, the button is also the small blind and acts first preflop. Rule 36C of the [Poker TDA Rules 2026, Version 1.1, 21 September 2026](https://www.pokertda.com/view-poker-tda-rules/) also says that the button receives the last card and acts last on every later betting round. The button may be adjusted when heads-up play begins.

Here, the small blind is 0.5 bb and the big blind is 1 bb. Lowercase **bb** means a big-blind unit; **BB** identifies the player’s position. BTN and SB refer to the same player at this table. A room may set its own order, so check the rules where you play.

An open to 2.5 bb means a total raise to that amount, not another 2.5 bb on top of the small blind. That distinction matters when comparing calculations: are you counting the whole attempt or only the decision after posting the compulsory blind?

## How wide to open

The sources suggest opening **70–85% of combinations**, but these are authors’ practical recommendations, not solver frequencies. Treat the interval as a starting point rather than a fixed range against every opponent. The same opening range can face very different frequencies of folds, calls and 3-bets.

Upswing Poker, 24 February 2017, upswingpoker.com, recommends opening 70%+ and describes a default of about 85% with a raise to 2.5 bb. DeucesCracked, date not stated, deucescracked.com, suggests 70–85%. Neither percentage automatically identifies which hands belong in your range.

| Share of range | Combos out of 1326 |
|---|---:|
| 65% | 862 |
| 70% | 928 |
| 75% | 995 |
| 80% | 1061 |
| 85% | 1127 |
| 90% | 1193 |
| 91% | 1207 |

These percentages measure shares of starting-hand combinations, not shares of hand types on a range chart. Pairs, suited hands and offsuit hands represent different numbers of combinations. Selecting the same number of chart cells therefore does not necessarily produce the same range width. Combo counts in this table are rounded to whole numbers.

Use the [poker range builder](https://toolsgambling.com/poker/range-builder) to compare range composition with its share of combinations. Decide which hands you want to include, then assess the total width rather than filling arbitrary cells to reach a percentage. For position labels such as BTN, SB and BB, or notation such as 22+, see [how to read preflop range charts](https://toolsgambling.com/blog/poker-hand-ranges-preflop-charts).

## Open size

The sources’ usual starting point is a raise to **2–2.5 bb**, adjusted alongside range width to the BB’s response. For a no-equity hand at 2.5x, the fold threshold against folding is 57.1% (the “vs folding” columns), while the threshold against zero is 71.4% (the “vs zero” columns). Defense means the share of occasions on which the BB does not fold.

In the table, 2x means a raise to 2 bb. “Defense” means the share of occasions on which the BB does not fold; it is not a ready-made calling range. The “vs folding” columns treat the already posted small blind as the cost of folding; the “vs zero” columns do not.

| Open size | Fold threshold: vs zero | BB defense: vs zero | Fold threshold: vs folding | BB defense: vs folding |
|---|---:|---:|---:|---:|
| 2x | 66.7% | 33.3% | 50.0% | 50.0% |
| 2.25x | 69.2% | 30.8% | 53.8% | 46.2% |
| 2.5x | 71.4% | 28.6% | 57.1% | 42.9% |
| 3x | 75.0% | 25.0% | 62.5% | 37.5% |
| 3.5x | 77.8% | 22.2% | 66.7% | 33.3% |

![Diagram: big-blind fold threshold for 2x, 2.5x and 3x button opens heads-up: vs zero 66.7%, 71.4% and 75%; vs folding 50.0%, 57.1% and 62.5%.](https://toolsgambling.com/media/article/2026/10/80141ab859e6f48d34c7f9a1cb1a43d3.webp)
*Educational calculation: the share of big-blind folds at which a button open with no equity breaks even, measured against zero and against folding. Not a solver output and not a third-party interface.*

When the BB folds often, the smaller size performs better on these numbers. At **70% folds**, a 2x open returns **+0.10 bb** per attempt, while 2.5x returns **−0.05 bb**, relative to zero. Against folding (−0.5 bb), the same 70% gives **+0.60 bb** for 2x and **+0.45 bb** for 2.5x. This comparison assumes a no-equity hand and an unchanged opponent response; it does not establish that smaller raises are better for every hand.

When the BB defends often, a larger raise with a tighter range is the sensible choice. Upswing Poker recommends 2x–2.25x against frequent folds and 2.5x–3x against frequent defense. That advice points in the same direction, but the EV figures here are our calculation. Increasing the size alone does not repair a weak range, and the BB may respond differently to the new size.

## How to calculate the expectation

The expected value of an open depends on the BB’s fold frequency, the total raise amount and the hand’s equity against the BB’s calling range. The simplified calculation is:

**EV = f · 1 + (1 − f) · X · (2e − 1)**

The variables are:

- **f:** the BB’s fold share;
- **X:** the total open size in bb;
- **e:** the hand’s equity against the BB’s calling range;
- **EV:** the net result in bb per attempt.

When the BB folds, the button wins the big blind for a result of **+1 bb**; the button’s own small blind is returned, not counted as winnings. When the BB calls, the calculation allocates the pot by equity without further betting. This separates the effect of the assumptions rather than predicting the outcome of a complete hand.

For a hand with no equity, the results relative to zero are:

| BB fold share | EV at 2x, bb | EV at 2.5x, bb | EV at 3x, bb |
|---|---:|---:|---:|
| 30% | −1.10 | −1.45 | −1.80 |
| 50% | −0.50 | −0.75 | −1.00 |
| 60% | −0.20 | −0.40 | −0.60 |
| 70% | +0.10 | −0.05 | −0.20 |
| 80% | +0.40 | +0.30 | +0.20 |

For example, you open to **2.5 bb** and the BB folds half the time. Assume your hand has no equity when called. Half the attempts return +1 bb and the other half lose 2.5 bb, producing **−0.75 bb per attempt** relative to zero. This example uses the whole-attempt accounting above; EV is displayed to the precision shown in the tables. Against folding (−0.5 bb), this is 0.25 bb worse, so a no-equity open at 50% folds does not beat folding.

At 50% folds, an open with no equity is worse than folding: −0.75 versus −0.5 bb. Equity changes the result, however. The table below, for the same 2.5x open and 50% folds, is relative to zero. Every row from −0.25 bb upward beats folding (−0.5 bb), so roughly 10% equity is enough for the open to beat folding (EV −0.5 bb). The 30% row, where EV crosses zero, is break-even against zero, not against folding:

| Equity against the BB calling range | EV, bb |
|---|---:|
| 10% | −0.50 |
| 20% | −0.25 |
| 30% | 0 |
| 40% | +0.25 |
| 50% | +0.50 |
| 60% | +0.75 |

Equity means the expected share of the pot at showdown, including a proportional share of ties. It is not simply the percentage of outcomes won outright. A small positive EV in this table is also not enough to select a precise opening chart: changing the fold frequency or the composition of the calling range can change the sign of the result.

## Why the published numbers disagree

The percentages disagree because they describe different decisions and use different accounting assumptions. A bluff’s break-even fold frequency, a minimum defense frequency and a practical BB continuing range are not interchangeable.

| Source | Number | What it measures |
|---|---|---|
| PokerNews | About 30% | Defense against an opponent about whom nothing is known; a recommendation, not a threshold |
| PokerNews | 37.5% | Defense against an opponent who opens 100% of hands to 3 bb; matches the fold threshold against folding at 3x (62.5% folds) |
| DeucesCracked | 55–65% | Defense that considers hand equity, not a no-equity hand’s fold threshold |
| Calculation against zero | 28.6% | Defense against zero at 2.5x (break-even 71.4%) |
| Calculation against folding | 42.9% | Defense at 2.5x against folding (threshold 57.1%) |

PokerNews, 13 February 2010, updated 10 November 2022, pokernews.com, recommends opening roughly 70–80% to 3 bb. Its “invest 2.5 to win 1.5” reasoning produces a 62.5% fold threshold against folding at 3x. Its “about 37.5%” defense applies to an opponent who opens 100% of hands to 3 bb (see the table).

Why 62.5% and 75.0% at 3x? Both are correct for different questions. 62.5% is the threshold against folding; 75.0% is break-even against zero. The 12.5-point gap is the cost of folding: the 0.5 bb the button has already posted. Choose the reference point before comparing numbers.

The formulas make the distinction explicit:

- Break-even fold threshold vs zero: **X / (1 + X)**.
- Defense vs zero: **1 / (1 + X)**.
- Fold threshold vs folding: **(X − 0.5) / (1 + X)**.
- Defense vs folding: **1.5 / (1 + X)**.

[GTO Wizard, “MDF & Alpha”, 1 July 2022](https://blog.gtowizard.com/mdf-alpha/) explains minimum defense frequency (MDF) and break-even fold frequency (alpha). For an initial bet, the formulas are **pot / (bet + pot)** and **bet / (bet + pot)** respectively. The author notes that these formulas work only for an initial bet and uses risk / (risk + reward) for a raise. Our “vs folding” columns follow that form: risk X − 0.5 bb, reward 1.5 bb. MDF is a heuristic, not a universal instruction to call.

First check what the source uses as its base. Do not substitute the 55–65% defense for a threshold: it considers hand equity.

## Limits and mistakes

The tables are limited to an **effective stack of 100 bb** — our assumption; the sources do not state a depth — and do not describe a complete heads-up strategy. The effective stack is the amount the players can risk against one another, limited heads-up by the smaller stack.

The concrete boundaries are:

- **No postflop play.** The calculation allocates the pot by equity without future bets, folds or differences in equity realization.
- **No BB 3-bet in the call branch.** Continuing is represented by a call. Actual defense can include raises, so total continuation frequency is not the same as calling frequency.
- **No rake.** A deduction from the pot changes the result of marginal decisions.
- **Equity is measured against the calling range.** Equity against all random starting hands answers a different question. When the BB folds weaker holdings, the remaining range changes.
- **No solver chart.** We did not find one and do not present the authors’ recommendations as solver frequencies.

DeucesCracked also cites a BB 3-bet frequency of 12–18%. Do not mechanically add it to this calculation: that branch needs separate button decisions and raise sizes. The continuation of that betting sequence is covered in [4-bet vs 3-bet](https://toolsgambling.com/blog/four-bet-preflop).

The claim that “folding more than 30% of buttons is a leak” is also DeucesCracked’s position. It does not establish that every hand beyond that boundary should be raised against every BB. Size, opponent response and the later betting decisions remain part of the choice.

Do not transfer [6-max opening ranges](https://toolsgambling.com/blog/6-max-poker-cash) directly to heads-up. The positional structure is different, so the frequencies cannot simply be reused. Likewise, a defense frequency of 28.6% against zero (about 379 combos out of 1326) is a threshold under specific accounting assumptions, not a list of hands to call.

The tables do not promise profit, and the calculation is not a guarantee of results.

## What to check before using the tables

First, find the opening size in the source and confirm that it means a raise to that amount, not an increase over the blind. Then compare the accounting reference point, the price of a call and the assumed BB response.

For the big blind’s decision, the [pot odds calculator](https://toolsgambling.com/poker/pot-odds) helps compare the price of calling with the required equity. That is a different question from how often the BB must fold for the button’s bluff to break even. A low defense threshold alone does not identify which hands make worthwhile calls.

For the distinction between the current price of a call and possible future winnings, read [pot odds and implied odds](https://toolsgambling.com/blog/pot-odds-implied-odds-poker). Future winnings are not included in the tables above, so they cannot silently be used to justify a positive result in this formula.

Before choosing a range, verify three conditions: the raise amount is the total size; equity is measured against the calling range; and the call calculation excludes BB 3-bets.

## FAQ

### What size should I open to from the button heads-up?

The sources usually suggest 2–2.5 bb. Choose with the BB’s fold frequency in mind; the size table compares the break-even thresholds.

### How many hands should I open from the button?

The sources suggest 70–85% of combinations, not hand types. For example, 70% represents about 928 combos out of 1326.

### Why do the sources give different BB defense numbers?

30% is defense against an unknown opponent; 37.5% is defense at 3x against an opponent who opens 100% of hands; 55–65% is defense that considers hand equity.

### Is this a GTO chart for heads-up?

No. We did not find a solver chart. The tables calculate opening EV under stated fold and call assumptions, rather than solve a complete heads-up strategy.