Made Another Payment!

I love paying down my mortgage.  I’m just 4 months ahead of pay off schedule at this point, and I plan to pay off the mortgage at least 5 years early so I can retire without a house payment.
How am I gonna do this?  By paying $250 extra a month in principal.  I’m not sure how much interest it will save me, but I’ll figure that out another time.
As of 7/15/16, I owed $79,070.13.  (Ok I’m dropping dollar signs “$” from here).
Of the 900 mortgage payment I made August 1, 344.54 went to principal (232.27 went to interest, and 323.19 went to Escro, which is tax and insurance).
Then, I paid an additional 250 in principal so I currently owe 78,725.59.
– – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – —
A question that arises is . . .
at this rate, about when will I be at 70K?
Let’s round the numbers a bit and say I pay 350 plus 250 a month for principal.  That’s 600 a month.  Subtract 600 a month from 78,725.59 and it’ll take 15 months.  Fifteen months from now is Nov 2017.
 
Alright, let’s see if I can keep up the extra 250 and celebrate 70K late next year.