OK, so let's say your monthly benefit is $2000.
You earn $6,667/mo at your job from Jan-April, or $26,667 during those 4 months.
The earnings limit that year is higher than before. In 2015 it is 41,880. (2016 is similar).
So, for earnings test purposes, you will have no reduction.
Because you will NOT earn over $41,880 between Jan and April, you are NOT exceeding the yearly limit, as it only applies to those months before full retirement age.
You can see an example of this further, by reading here (and scrolling down on the page).
However, your actual benefit owed will be a small % reduced, due to choosing to collect early. It should be reduced by 5/9 of 1% for each month you take early. SO if you are taking 4 months early, that would be 4*5/9*1% or 20/9 *1% = about 2.2% reduction. So if your benefit should have been 2000, it will be permanently reduced by about $44.5 per month to $1955.56.