Right, that is simple math. But what if the 49ers beat the Seahawks (who win out the other games) but lose to the Rams. If both at 12-4, who takes the division?
In that scenario it's the 5th tiebreaker which is strength of victory, which I don't know if we can determine yet.
Reason it's the 5th.
First tiebreaker is head to head, they split.
Second is record in division. They'd have each lost twice, once to each other and once each to the Rams.
Then you have record in common games. They've both lost to Baltimore, Seattle beat Atlanta but lost to New Orleans. San Francisco beat New Orleans but lost to Atlanta.
Next is record in conference. Both would have lost 3 games within the NFC.
So then you have strength of victory. (w/l/t percentage of opponents)
As of right now, the total wins of all Seattle's opponents is 72. The total wins of all of San Francisco's opponents is 67. (I'm ignoring ties since their only opponent with ties was the Cardinals whom they both play twice) Also, if New Orleans wins tonight this benefits the 49ers over the Seahawks.
However, if Seattle beats Cardinals next week they add only 4 victories to 76, but if San Fran wins the rematch then they're add the 12 that Seattle would have to 79. But you have to consider that their opponents they've beaten are still playing those 2 weeks as well and could affect the outcome.
Edit: If somehow through freak occurrence the 5th tiebreaker doesn't settle it (possible because SF beat Redskins and Green Bay who Seattle didn't play, Seattle beat Eagles and Minnesota who SF didn't play. Also if somehow over the final 2 games Atlanta has a better record than New Orleans). Then you go to the 6th tiebreaker which is a lock for Seattle. The 6th tiebreaker is Strength of record. So w/l/t percentage of all opponents, not just those you beat. Seeing as 3 of their 4 losses would have the exact same record, that adds nothing. But Seattle gets to add New Orleans record to their strength while SF would add Atlanta. New Orleans is guaranteed a better record than Atlanta this season.