Raising rents in a 4 plex

[John Kilhafner]

Looking to raise rents in a 4 plex to near area average, the property was purchased a couple months ago and each unit is well below market.  My thoughts were to send a letter letting the tenants know that the rents will be raised at the 1st of the year to give them time to decide to stay or find another apartment.  Trying to figure out if a 25% increase is to much, which is only $100 but I understand this is a lot of money to some.  Similar units in this area range from $525 to $600 a month, I figured I would make the initial jump to $500 then slowly raise to market price.  Any advice or things I might be missing here would be appreciated.