
Tim C. answered 03/30/19
Former math teacher - math, CS, and science tutor
The formula you entered is compounding every month, not every quarter, which earns you an additional .5% each year.
Something like =pmt(RATE/4,NPER*4,0,25000)/3 gets you closer to the answer you wanted. This means you pay January 1, February 1, and March 1, then when you pay April 1 the interest for your first 3 payments is added to the balance.
The answer you wanted assumes you pay January 1, February 1, and when you make your March 1 payment, the interest for your first 2 payments is added to the balance, but I can't immediately think of how to use the PMT function to arrive at that exact answer.