# Drilling Doubles: The Hands Worth Twice the Bet

Every doubling cell in a blackjack basic strategy chart, counted: the 47 doubles in the multi-deck S17 chart, what other deck counts and soft 17 rules add, and how to drill the borders.

Source: https://21trainer.app/articles/drilling-doubles/
Updated: October 19, 2026
Publisher: 21 Trainer, makers of Blackjack Strategy: 21 Trainer, an educational blackjack trainer for iPhone and Android (App Store: https://apps.apple.com/app/blackjack-strategy-21-trainer/id6759527695, Google Play: https://play.google.com/store/apps/details?id=app.blackjacktrainer)

> **Educational content, not gambling advice.** 21 Trainer and this article teach blackjack strategy and card counting as skills, using virtual chips only. No strategy or counting system guarantees winnings, and nothing here encourages real-money play. If gambling is a problem for you or someone you know, call 1-800-522-4700 (National Council on Problem Gambling).

Every basic strategy chart holds a short list inside it: the cells where the right play is to double the bet and take exactly one more card. In the four to eight deck chart where the dealer stands on soft 17, that list is exactly 47 of the 280 cells. That is 16.8 percent of the chart (47 divided by 280), a block small enough to know cold.

This piece is that list, cell by cell, plus what the other rule sets add and a plan for drilling the edges. The reasoning lives elsewhere: our guide to [when to double down](https://21trainer.app/articles/when-to-double-down/) explains why these hands justify a second bet, and the single-row pieces on [hard 11](https://21trainer.app/articles/hard-eleven-doubling/), [hard 10](https://21trainer.app/articles/hard-ten-doubling/) and [hard 9](https://21trainer.app/articles/hard-nine-doubling/) cover the individual totals. Here the job is inventory and recall, with one wording note: the soft 18 doubling cells in this chart read double if allowed, otherwise stand, and every other doubling cell reads double if allowed, otherwise hit.

## The 47 cells, row by row

Here is every doubling row in the four to eight deck, dealer stands on soft 17 chart:

| Hand | Doubles against | Cells |
| --- | --- | --- |
| Hard 9 | 3, 4, 5, 6 | 4 |
| Hard 10 | 2 through 9 | 8 |
| Hard 11 | 2 through 10 | 9 |
| Soft 13 (A,2) | 5, 6 | 2 |
| Soft 14 (A,3) | 5, 6 | 2 |
| Soft 15 (A,4) | 4, 5, 6 | 3 |
| Soft 16 (A,5) | 4, 5, 6 | 3 |
| Soft 17 (A,6) | 3, 4, 5, 6 | 4 |
| Soft 18 (A,7) | 3, 4, 5, 6 | 4 |
| Pair of 5s | 2 through 9 | 8 |

Three families make up the total. Hard 9 through 11 contribute 21 cells (4 plus 8 plus 9). The soft hands contribute 18 (2 plus 2 plus 3 plus 3 plus 4 plus 4). The pair of 5s contributes 8: its row matches the hard 10 row cell for cell. Add them, 21 plus 18 plus 8, and you get 47.

Notice what is absent: no hard total of 12 or more, and no soft 19 or soft 20, doubles in this chart. Two of those absences hold in all six of the app's charts: none of them doubles a hard 12 or higher, and none doubles soft 20.

## Four rules of thumb, and where they bend

Four sentences summarize this chart:

- **Hard 11 doubles against everything but an ace.**
- **Hard 10 doubles against 2 through 9.**
- **Hard 9 doubles against 3 through 6.**
- **Soft hands double only against weak upcards, and the band widens as the soft total rises from A,2 to A,7.** A,2 and A,3 double only against 5 and 6; A,4 and A,5 stretch to 4 through 6; A,6 and A,7 stretch to 3 through 6.

One companion rule completes the soft side: A,7 that cannot double stands. Those four soft 18 cells are the only doubling cells in this chart whose fallback is a stand rather than a hit. Every other refused double becomes a hit.

Where they bend, chart by chart: hard 10 against 2 through 9 holds in all six of the app's charts. Hard 11 also doubles against an ace in the other five. Hard 9 starts at 2 instead of 3 with 2 decks or 1 deck. On the soft side, A,7 reaches down to 2 when the dealer hits soft 17 with 4 to 8 decks or 2 decks, and A,3 reaches 4 in the 2 deck version of that rule. In the 1 deck charts A,2 and A,3 reach 4 and A,6 reaches 2, so there A,6 doubles against one more upcard than A,7. The soft ladder and its logic are covered in our introduction to [soft hands](https://21trainer.app/articles/soft-hands-blackjack/).

## What the other charts add

Measured against the chart above, every other chart in the app keeps all 47 doubles and adds a few:

| Chart | Double cells | Added doubles |
| --- | --- | --- |
| 4 to 8 decks, S17 | 47 | the baseline above |
| 4 to 8 decks, H17 | 50 | hard 11 against an ace, soft 18 against 2, soft 19 (A,8) against 6 |
| 2 decks, S17 | 49 | hard 9 against 2, hard 11 against an ace |
| 2 decks, H17 | 52 | hard 9 against 2, hard 11 against an ace, soft 14 against 4, soft 18 against 2, soft 19 against 6 |
| 1 deck, either rule | 55 | hard 8 against 5 and 6, hard 9 against 2, hard 11 against an ace, soft 13 and soft 14 against 4, soft 17 against 2, soft 19 against 6 |

Soft 18 against 2 and soft 19 against 6 read double if allowed, otherwise stand; every other addition reads double if allowed, otherwise hit. The growth runs from this baseline only: going from 2 decks to 1 deck with the dealer hitting soft 17, for one, drops soft 18 against 2. Our cell by cell comparisons of [single deck](https://21trainer.app/articles/single-deck-chart-differences/) and [double deck](https://21trainer.app/articles/double-deck-chart-differences/) charts set these doubles beside the split and surrender changes, and [S17 versus H17](https://21trainer.app/articles/s17-vs-h17/) covers the soft 17 rule itself.

One quirk sits in the pair rows: in the one deck charts, 4,4 against a 5 and a 6 is marked split with double after split, otherwise double. So at a one deck table without double after split, the pair of 4s adds two more doubles to the count above.

## How often the decision actually arrives

The doubling block is 16.8 percent of the chart but a smaller share of the game. Per our simulation of about 62 million six-deck rounds, described in [how often you win a blackjack hand](https://21trainer.app/articles/how-often-you-win-a-hand/), a round included a double 10.27 percent of the time, about one round in ten.

In the same simulation, a doubled hand won 55.17 percent of the time, pushed 6.94 and lost 37.89, against 43.53 percent of all hands won. Those are long-run averages under one fixed set of rules, not a forecast for a session.

## When the table restricts doubling

Some tables allow doubles only on hard totals of 9, 10 and 11, or on 10 and 11 only. The full story is in our piece on [tables that only let you double on 9, 10 or 11](https://21trainer.app/articles/double-restrictions-9-10-11/); the effect on the count is arithmetic.

Under the 9, 10 and 11 rule, every soft double cell falls back: soft 13 through soft 17 become hits, and soft 18 becomes a stand. That removes all 18 soft cells from the list, leaving 29. Under the stricter 10 and 11 only version, the 4 hard 9 cells go too, leaving 25 (21 minus 4, plus the 8 cells for 5,5, which qualifies as a hard 10). Hard 10, hard 11 and 5,5 survive both versions, but a player who has drilled all 47 cells now needs a shorter second list for these tables.

## Drilling the borders

The app cannot restrict a drill to doubling hands or to any other single category, so the 47 cells are learned in two stages. First with the chart itself, reading the families above as sentences and borrowing the methods from our pieces on [mixed versus blocked practice](https://21trainer.app/articles/mixed-hand-drills/) and [soft hand recognition](https://21trainer.app/articles/soft-hand-recognition-drill/): classify the hand first, then give the play.

Then the list is tested in the app's mixed practice, where every decision gets instant feedback with an explanation. A useful focus is the borders: for each row, the upcard where doubling starts and the upcard where it stops. Hard 9 starts at 3; hard 10 stops at 9; the soft rows creep wider from A,2 to A,7. Most of the exceptions in the chart table sit right on these borders (hard 9 against 2, hard 11 against an ace, A,7 against 2), and a wrong answer on a border cell tells you which family to reread.

The Pro upgrade adds two tools that fit this job: the Weakness Drill, which finds and drills your weakest hands, and accuracy heat maps by hand type and dealer upcard, which show whether errors cluster on the doubling rows or somewhere else entirely. The borders you keep missing become a named list to take back to the chart. Fitting doubled hands into a longer routine is covered in our [four week practice schedule](https://21trainer.app/articles/blackjack-practice-schedule/), which puts soft hands and doubling in week 2.

## Frequently asked questions

### How many doubling hands are in blackjack basic strategy?

In the four to eight deck chart where the dealer stands on soft 17, exactly 47 cells out of 280 call for a double: 21 hard cells (hard 9, 10 and 11), 18 soft cells (soft 13 through soft 18) and 8 cells for a pair of 5s, which plays as a hard 10. The app's other five charts keep all 47 and add between 2 and 8 more.

### Do you ever double down on soft 19 or soft 20?

Not in the four to eight deck chart where the dealer stands on soft 17. Soft 19 (ace, 8) against a 6 reads double if allowed, otherwise stand in four of the app's six charts: 4 to 8 decks and 2 decks when the dealer hits soft 17, and both 1 deck charts. Soft 20 stands against every upcard in all six.

### What happens to doubling when the table only allows it on 9, 10 and 11?

The rule counts only hard totals of 9, 10 and 11, so every soft double disappears. That removes 18 of the 47 cells in the four to eight deck chart where the dealer stands on soft 17, leaving 29: soft 13 through soft 17 fall back to a hit, soft 18 to a stand. Under the stricter 10 and 11 only version, the 4 hard 9 cells go too, leaving 25 doubles.

### Should you split or double a pair of fives?

Double. In all six of the app's charts, 5,5 plays exactly like hard 10: double if allowed, otherwise hit against 2 through 9, and hit against a 10 or an ace. No cell in the 5,5 row of any of those charts calls for a split.

### How often does the chance to double come up in blackjack?

Roughly one round in ten. In our simulation of about 62 million six-deck rounds, a round included a double 10.27 percent of the time, and the doubled hands won 55.17 percent of the time, pushed 6.94 and lost 37.89. Those are long-run figures for basic strategy, not a promise about any session.

## Keep reading

- [When to Double Down in Blackjack](https://21trainer.app/articles/when-to-double-down/)
- [Soft Hands: Why Ace-Six Is Not a 17](https://21trainer.app/articles/soft-hands-blackjack/)
- [Tables That Only Let You Double on 9, 10 or 11](https://21trainer.app/articles/double-restrictions-9-10-11/)