m wrote...
Please find the following simulations, which proofs that PMT() uses 360-Days
Bases.

Installment Mode - Advance
Simulation - 1
Loan Amount 349,300.00
IRR 12.50%
Tenor 60 Mths
Using PMT() (360-Days Bases) 7,777.51
Manual Calculation (365-Days Bases) 7,778.65 (Desired Result)
Difference 1.14

On my machine, Excel 2003 accepts the formula

=PMT((1.125)^(1/12)-1,60,-349300,,0)

and evaluates it as 7,741.12, and it accepts the formula

=PMT(0.125/12,60,-349300,,0)

and evaluates it as 7,858.53. What are the EXACT formulas you're
using?

Simulation - 2
Loan Amount 872,000.00
IRR 13.99%
Tenor 12 Qtrs
Using PMT() (360-Days Bases) 87,186.00
Manual Calculation (365-Days Bases) 87,196.89 (Desired Result)
Difference 10.89

=PMT((1.1399)^(1/4)-1,12,-872000,,0) returns 89,325.28

=PMT(0.1399/4,12,-872000,,0) returns $90,224.73

Again, what are your EXACT formulas? What are your IRRs? Do they
actually include more decimal places than you're showing here?