Cheers - we're getting there. Unfortunately, something else is broken since
it no longer correctly calculates the correct number of payments, in D6 or
Rows 18 and lower.

Your assistance is greatly appreciated, Gordon. Thanks again.

As I'm involved in the mortgage industry, I was rather intrigued by the OP's
statement that he was making weekly mortgage payments.  While 20 or more
years ago some lenders were offering bi-weekly mortgages, those were quickly
abandoned.  The vast majority of mortgage loans demand *monthly* payments
and interest is calculated on a *monthly* basis.  While there are a number
of services which will make weekly *withdrawals* from your account, the
actual *payments* are made on a monthly basis.  If the OP has a true weekly
mortgage, he has a rare bird indeed.

That having been said, the difficulties that he is experiencing with trying
to use that template for weekly payment calculations lies in the fact that
the template is still making the assumption that pmts are expected on a
monthly basis and that interest is calculated on a monthly basis.
To illustrate: a $300,000 loan for 30 years at 5% will have a monthly pmt of
1610.46; total number of pmts is 360.
Entering in B19 =IF(Pay_Num<>"",DATE(YEAR(B18),MONTH(B18),DAY(B18)+7),"")
if you then substitute in D11 the first formula you suggested:
=IF(Values_Entered,-PMT(Interest_Rate/52,Loan_Years*52,Loan_Amount),"")
you'll come up with a "weekly" pmt amt of 371.39 which is reasonable -- only
about 0.25 short of (1610.46*12) / 52.  And the scheduling shows a weekly
progression.  So far, so good.
HOWEVER, one quickly notices that the Principal Payment column shows
negative
figures and the ending balance *increases* as "pmts" are made.
If you substitute in D11
=IF(Values_Entered,-PMT(Interest_Rate/12,Loan_Years*52,Loan_Amount),"")
your "weekly" pmt increases to 1251.91 which is roughly the monthly amount
prorated to a pmt every 23 to 24 days.   Even though not a weekly amount,
it's better ---  but still not good enough, as you'd be paying down your
principal vastly more slowly than standard monthly pay-down.
You'll notice also, in both cases, that the scheduled number of pmts for
this loan, even though  ostensibly scheduled on a weekly basis, still number
only 360, rather than the 1560 you'd expect for 30 years.
The underlying problem lies with the template's assumption of monthly
payment expectations and monthly interest calculation.
--
alan

See my other reply....