The following chart shows the heads-up winning percentages for most common matchups you will find yourself in a holdem game. The first number under each card hand is the winning percentage and the number in parenthesis is the odds. For example, the second column represents how AK would fair in heads-up match against various hand combinations. To see how AK matches up against an underpair such as TT, look at the second row. You will see that AK will win 43% of the time against TT and the odds against winning are 1.3 to 1. To determine how a medium pair like 88 would stack up against an over pair like TT, look at the second to last column labeled Medium Pair and move down to the first row. You will see that 88 will win only 17% of the time against TT and the odds against winning are 4.7 to 1.
 
Pair

Premium Non Pair

Ace + Low Kicker
2 Picture Cards
Medium Pair
Rags
 
A A
A K
A 5
Q J
8 8
7 2
PAIRS
over
A A 15%
(5.7 to 1)
T T 17%
(4.7 to 1)
9 9 10%
(8.8 to 1)
under
T T 81%
(6.2 to 1)
T T 43%
(1.3 to 1)
3 3 46%
(1.2 to 1)
9 9 45%
(1.2 to 1)
5 5 81%
(0.2 to 1)
between
T T 30%
(2.4 to 1)
5 5 27%
(2.7 to 1)
NON PAIRS

2 over cards

A K 34%
(1.9 to 1)
A J 55%
(0.8 to 1)
A T 32%
(2.2 to 1)

2 under cards

T 9 81%
(0.2 to 1)
T 9 63%
(0.6 to 1)
3 2 68%
(0.5 to 1)
8 7 65%
(0.5 to 1)
6 5 84%
(0.2 to 1)

1 over, 1 between

T 5 35%
(1.9 to 1)

1 over, 1 under

A 9 43%
(1.3 to 1)
T 5 70%
(0.4o 1)

2 between

T 9 55%
(0.83 to 1)
5 4 48%
(1.1 to 1)

1 matching, 1 over

A K 25%
(3.0 to 1)
K Q 25%
(3.0 to 1)
A 8 68%
(0.5 to 1)
A 7 21%
(3.8 to 1)

1 matching, 1 under

A K 92%
(0.1 to 1)
8 7 85.3%
(0.2 to 1)
* None of the unpaired cards we used in the analysis were suited. For suited cards assume a winning % of an additional 2.4%. Connecting cards such as T9 versus non-connecting cards such as T5 also have an advantage of just a few percentage points.