Last Updated: November 4, 2019

# Over/Under 13

## Introduction

Over/Under 13 are a pair of side bets on whether the player's first two cards will total under or over 13. The bets have been around since the 1980's at least and I believe to be among the first blackjack side bets.

## Rules

1. Both side bets are based on the sum of the player's initial two cards.
2. Aces count as one point.
3. Both the Over 13 and Under 13 bets lose on a total of 13.
4. Wins on both bets pay even money.
5. The Majestic casino in Panama City offers a bet on a total of exactly 13, which pays 10 to 1.

## Analysis

The following table shows the probability of winning and house edge of the Under 13 bet.

### Under 13

Decks Probability House Edge
1 44.95% 10.11%
2 44.96% 10.08%
4 44.97% 10.07%
6 44.97% 10.07%
8 44.97% 10.06%

The following table shows the probability of winning and house edge of the Over 13 bet.

### Over 13

Decks Probability House Edge
1 46.61% 6.79%
2 46.68% 6.65%
4 46.71% 6.58%
6 46.73% 6.55%
8 46.73% 6.54%

The following table shows the probability of winning and house edge of the Exactly 13 bet at a win of 10 to 1.

### Exactly 13 — Wins pay 10 to 1

Decks Probability House Edge
1 8.45% 7.09%
2 8.36% 7.99%
4 8.32% 8.44%
6 8.31% 8.58%
8 8.30% 8.66%

## Card Counting

Both Under 13 and Over 13 bets are highly vulnerable to card counting (shut up Wiz!). For an thorough treatment of the topic, I recommend Professional Blackjack by Stanford Wong. He covers the topic in chapter 11 of the 1994 edition.

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