# Side Counting Aces, and Why Most Systems Skip It

An ace side count is a second tally of aces seen versus expected, kept beside the main count to sharpen betting decisions. Here is why Hi-Opt and Omega II use one, and why most counters skip it.

Source: https://21trainer.app/articles/side-counting-aces/
Updated: September 23, 2026
Publisher: 21 Trainer, makers of Blackjack Strategy: 21 Trainer, an educational blackjack trainer for iPhone (https://apps.apple.com/app/blackjack-strategy-21-trainer/id6759527695)

> **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).

Walk past a busy blackjack table and imagine the numbers in each head. Most counters are holding one: the running total of their system, updated card by card. A small minority are holding two. Underneath the main count, in a separate mental register, they are tracking aces: how many have appeared against how many the shoe should have produced by now, a number that exists only to refine what the main count says about the money, not the cards.

That second register is an ace side count, and it is the signature of a whole family of counting systems. It is also, for most people who count, a bad trade. This article covers both halves honestly: why some systems want the ace counted separately at all, and why the systems most recreational counters actually learn, Hi-Lo and KO among them, deliberately skip the extra work.

## The ace's two jobs

Most ranks in the deck have one effect on the game. The ace has two, and they pull in opposite directions. For betting, the ace is the raw material of the natural: blackjack pays 3:2, aces with tens make blackjacks, so a shoe rich in aces is a shoe in which the premium payouts arrive more often. That makes the ace one of the most valuable cards in the deck from a betting standpoint. For playing decisions, the same ace behaves more like a small card: drawn to a stiff hand it counts as one and cannot bust you, and it is what turns a hand soft. Many hit, stand and double decisions care little whether aces are dense or sparse.

A main count is a single number asked to serve both jobs, and every published system takes a position on that compromise. The [Hi-Lo count](https://21trainer.app/articles/hi-lo-card-counting/) tags the ace minus one, grouped with the tens. The [KO count](https://21trainer.app/articles/ko-count-system/) does the same. [The two Hi-Opt systems](https://21trainer.app/articles/hi-opt-i-and-hi-opt-ii/) refuse: both tag the ace exactly zero, on the argument that the ace's power is mostly about getting paid on naturals, a betting concern, while the business of deciding whether to hit, stand or double is better served by a count that ignores aces entirely. [Omega II](https://21trainer.app/articles/omega-ii-count-system/) makes the same choice at level two. And [the Zen count](https://21trainer.app/articles/zen-count-system/) splits the difference, giving the ace a moderated minus one inside the main count while the tens carry minus two.

That tag table is the whole origin of side counting. An ace-neutral count throws away the ace's betting information on purpose, to keep the playing signal clean. A side count is how a player picks that information back up without putting it back into the main number.

## What a side count actually is

Mechanically, an ace side count is a second tally, kept alongside the main count, of aces seen versus aces expected. The expectation comes from simple pace: four aces sit in every fifty-two cards, so on average one ace arrives per quarter deck. Quarter deck by quarter deck, the counter compares the two numbers. A surplus of aces gone from the shoe ahead of pace means the remaining shoe is ace poor; a shortage gone means it is ace rich.

What the comparison is for matters as much as the tally itself. The side count adjusts betting decisions. It does not change playing decisions, which continue to key off the main count and its indices, because the main count is the one built for playing accuracy in the first place. How the two numbers are combined into a betting adjustment is defined by each published system for itself, and this article deliberately does not reproduce any formula or adjustment figures. What is worth internalizing is the shape: one number for the cards that matter to your hands, a second number for the card that matters to your naturals.

## What the second number is supposed to buy

The pitch for ace side counts is betting precision. A large share of the premium a counter works for comes from being paid on naturals, and naturals need aces, so a measure of ace density that the main count cannot see is, in principle, extra information about exactly the outcomes that pay best. Omega II is the standard illustration: with a maintained ace side count, its betting correlation is commonly described as near the practical ceiling, meaning the two numbers together track the shoe's favorability about as tightly as a practical count can. The gain over a single well-chosen number is real on paper, and modest.

## What it costs

The bill is paid in attention. A side count is a second continuous task running under table pace: it has to keep ticking while the main count updates on every card, while the dealer sweeps hands and deals the next round, and while the [division and deck estimation](https://21trainer.app/articles/running-count-vs-true-count/) that balanced counts require churn in the background. Layer index plays on top, and a counter with a side count is running three mental processes at once, at speed, for hours.

The failure mode is not subtle. Lose the main count for one hand and the evening's information is damaged; lose the side count and the betting adjustment is not merely missing, it is wrong, because an untracked surplus and an untracked shortage both look like zero. Our pieces on [holding a count while playing](https://21trainer.app/articles/count-and-play-at-the-same-time/) and on [recovering when the count drops](https://21trainer.app/articles/counting-errors-and-recovery/) describe how much of a counter's real skill is simply not losing tasks under load. A second tally doubles the surface area for exactly that failure.

This is the honest reason most recreational counters never adopt one, and it is a good reason. Hi-Lo and KO both include the ace in the main count, which means the ace's departure is already reflected, coarsely, in the one number being kept. The published comparisons of counting systems, as our [guide to choosing a system](https://21trainer.app/articles/choosing-a-counting-system/) summarizes them, commonly conclude that execution swamps system choice: a simple count run flawlessly outperforms an advanced count run with errors, and the side count premium is collected only by counters who can run the harder machine as cleanly as the easier one.

## The order to learn things in

For a player who does want a side count eventually, the counting literature is unusually consistent about the sequence. One count first: tags automatic, multi-card groups fluent, true count conversion comfortable, basic strategy so automatic that [playing and counting together](https://21trainer.app/articles/count-and-play-at-the-same-time/) costs nothing. Then index plays, one at a time. The ace tally comes last, layered on only when the main count no longer draws attention, which is the same position the Omega II article gives it in its own practice ladder.

A practical way to find out whether there is room in your attention for a second number: add one deliberately, in practice, and measure what happens to the first. If accuracy on the main count drops, the side count is costing more than it pays, and that answer does not change with enthusiasm.

One frame belongs here regardless of system. Counting cards with your head, side counts included, is legal in the United States. Casinos are private businesses that may refuse service to players they suspect of counting, so the skill carries no promise of a welcome. And no technique, single count or double, removes the risk from the game: counting at best offers a small long-run edge through large short-run swings, and losing sessions stay routine.

## Where the app fits

21 Trainer teaches four systems, Hi-Lo, KO, Omega II and Zen, with drills for each stage: single card tags, multi-card counting, true count practice, and index deviation training including the Illustrious 18. The bankroll simulator runs sessions with virtual chips so the counting skills can be practiced end to end with nothing at stake. The progression those drills encode is the one this article keeps repeating: one number, automatic, before any second number is allowed into the routine.

## Frequently asked questions

### What is an ace side count in blackjack?

An ace side count is a second tally kept alongside the main counting number, tracking how many aces have appeared compared with how many would be expected by that point in the shoe. It is used to sharpen betting decisions, not playing decisions, which still key off the main count. Systems that treat the ace as neutral in the main count, such as Hi-Opt and Omega II, use it to recover the ace's betting value.

### Why do some counting systems count aces as zero?

Because the ace has two different jobs. For betting it is the raw material of the 3:2 natural, one of the most valuable cards in the deck. For most playing decisions it behaves more like a small card, since drawn to a stiff hand it adds one point and cannot bust. Systems built for playing accuracy, like the two Hi-Opt counts, leave the ace at zero to keep that signal clean and track aces separately if at all.

### Should you learn an ace side count?

Not first, and for most recreational counters, not ever. A side count is a second number running under table pace, on top of true count conversion and any index plays, and published comparisons of counting systems commonly conclude that execution quality matters more than system choice. Learn one count until it is boringly automatic before layering any second task onto it.

### Is card counting with an ace side count illegal?

No. Counting cards with your head, side counts included, is legal in the United States. Casinos are private businesses that may refuse service to players they suspect of counting, and no counting technique removes the risk from the game. The activity is legal; the welcome is not promised.

### Does the Hi-Lo count need an ace side count?

No. Hi-Lo already assigns the ace a minus one tag inside the main count, so the ace's departure from the shoe is reflected in the running number itself. The same is true of KO. Side counts are the workaround used by ace-neutral systems such as Hi-Opt and Omega II; a count that includes the ace does not need one.

## Keep reading

- [Hi-Opt I and Hi-Opt II: Counts Built for Playing Accuracy](https://21trainer.app/articles/hi-opt-i-and-hi-opt-ii/)
- [Omega II: A Level-Two Count for the Ambitious](https://21trainer.app/articles/omega-ii-count-system/)
- [Hi-Lo vs KO vs Omega II vs Zen: Choosing Your System](https://21trainer.app/articles/choosing-a-counting-system/)