Child Benefit - can anyone tell me why

[taxattack]

For 2 children I receive £134.80/month when the benefit is stated on hmrc website to be £20.30 for dc1 and £13.40 for dc2? (that should total £146/mth)

Its paid 4 weekly.

There are 13 4 week periods in a year.

ok, that will total the £1752.40/year - thank you!