RATE function in VBA not working

rforster-10 

I agree with JKPieterse's workaround as the better solution.  WorksheetFunction.Rate (Excel RATE) is easier to use, and I suspect it is more reliable, in general.

But a minimal fix is to add a "guess" parameter, to wit:

interestRate = Rate(periods, payment, principal, futureValue, 0, 0.0080)

The zero is the "type" of the annuity, which you defaulted to zero.

0.0080 is 0.80%.  "Gee", you ask, "how did you know to use that guess?"

The payment must be large enough to cover the first period interest plus some principal.  Since the payment is 3419.65 and principal is 425000, the periodic interest rate must be less than 3419.65/425000 = 0.804623529411765%.

"But why", you ask, "does VBA Rate need a guess, but Excel RATE does not?"

Obviously, the internal algorithms are different, and presumably Excel RATE's algorithm is better.

IIRC, VBA Rate does indeed use a different method of approximation.  I believe that Excel RATE used the same method until Excel 2003, 2007 or 2010; I don't remember which.

But the bottom line is:  the VBA run-time error is equivalent to when Excel RATE returns #NUM (or #DIV/0).