One of my posts on enworld dissecting the 4E to-hit modifier.

http://www.enworld.org/forum/5061101-post14.html

Let's look at the pattern of to-hit roll modifier:

[level/2] + stat mod + magic enhancement = to-hit mod

starting with a minmaxed primary stat of 18 at level 1 (ie. stat mod of +4).

The magic enhancement follows the assumed pattern from page 225 from the 4E PHB:

level 1-5, enhancement = +1

level 6-10, enhancement = +2

level 11-15, enhancement = +3

level 16-20, enhancement = +4

level 21-25, enhancement = +5

level 26-30, enhancement = +6

The stat boosts are assumed to be added to the player's primary stat with enough stat boosts at levels 8, 14, 21, and 28, to affect the primary stat mod.

(stat mod = +4)

level 1, to-hit mod = +5

level 2-3, to-hit mod = +6

level 4-5, to-hit mod = +7

level 6-7, to-hit mod = +9

(stat mod = +5)

level 8-9, to-hit mod = +11

level 10, to-hit mod = +12

level 11, to-hit mod = +13

level 12-13, to-hit mod = +14

(stat mod = +6)

level 14-15, to-hit mod = +16

level 16-17, to-hit mod = +18

level 18-19, to-hit mod = +19

level 20, to-hit mod = +20

(stat mod = +7)

level 21, to-hit mod = +22

level 22-23, to-hit mod = +23

level 24-25, to-hit mod = +24

level 26-27, to-hit mod = +26

(stat mod = +8)

level 28-29, to-hit mod = +28

level 30-31, to-hit mod = +29

As an approximation, a possible replacement for [level/2] + stat mod + enhancement = to-hit mod

to-hit mod = level + 3, at heroic tiers of levels 1 to 10

to-hit mod = level + 2, at paragon tiers of levels 11 to 20

to-hit mod = level, at epic tiers of levels 21 to 30.

Not quite a single formula.

Looking at the patterns, I wonder whether it would be easier to just use a to-hit mod = +level, and changing the assumptions of the monsters and skills accordingly to acommodate this. The enhancement bonus of magic weapons for the to-hit and damage, could be stripped out with only the magical properties remaining which may be triggered by critical successes (or something else).

More generally, these approximate to-hit mod equations for a primary stat mod differing from +4 are:

to-hit mod = level + 3 + (primary_stat_mod - 4), at heroic tiers of levels 1 to 10

to-hit mod = level + 2 + (primary_stat_mod - 4) , at paragon tiers of levels 11 to 20

to-hit mod = level + (primary_stat_mod - 4), at epic tiers of levels 21 to 30.