Mortgage Formula

Trying to get a formula to automatically show a balance on a R/E Loan.
$140,000.00 Original Note @ 7.5% interest.
Paid 10% up front. ($14,000.00)
Starting 1/1/05, monthly pymts of $800.00.
How can I set up a formula to automatically reduce the balance of the loan after each monthly payment is made?
Thank you.

Thank you Old Chippy, but that is not what I was leaning toward.
I have a worksheet set up:
Column I-5 thru I-157 is the months numbered. (1 thru 157)
Column J-5 thru J-157 shows the months. (Jan. 2005 thru Sept. 2017)
Column K-5 thru K-157 shows $800.00 in each cell.
Column L-5 thru L-157 shows a running balance of monies paid in.
I was thinking of a "Lookup" formula that would take the original note of 140,000.00, less the 14,000.00 down, and have a cell to reflect the remaining balance of the note after each month's 800.00 pymt. I'm having a problem getting a "Lookup" formula to work here and I'm not sure why.

This is a simplified version of what I'm looking for.
Cell "B-5" will be where the balance owed on the loan will be shown. It should be automatically updated on the 1st of each month.
Thank you.

Thank you Oldchippy,
That will work fine.