Fred Smith wrote:
Canadian mortgages are compounded "every six months, not in advance".
So a mortgage quoted as 6% is actually 3% compounded semiannually.
If payments are anything other than semi-annual (which they almost
always are), you need to convert the quoted rate to a periodic rate,
as in:
=rate(annualperiods/2,0,-1,1+annualrate/2)

Obviously I know that since that is what I wrote in my updated posting,
which you quote. But that does nothing to improve my understanding
of the difference between "accel" v. "regular" weekly or biweekly
payment
schedules. No matter: I believe I discovered the answer myself.

Based on one online Canadian calculator, the rate() computation above
(and in my earlier posting) is useful for computing pmt() for "regular"
periodic payments. Thus, "regular" weekly/biweekly payments are
computed using normal amortization, assuming the payments go on
for the full loan term.

With "accel" weekly/biweekly schedules, the payment amount seems
to be based on the total monthly payments for 13 months (i.e. a year
plus one month), based the original loan term (e.g. 25 yr). That total
is divided by the number of "accel" payments (26 or 52). The "accel"
schedules are marketed as "allow[ing] you to make the equivalent of
13 months of payments over a 12-month period" -- similar to the way
semimonthly payments (at least) are marketed in the US. The effect
is to greatly reduce the total interest paid over the life of the loan,
as
well as to shorten the actual length of the loan.

For example, for a $100,000 Canadian loan at 6% over 25 yr nominally
the monthly payment is $639.81 for 300 payments and less than
$91,942 total interest, the "regular" biweekly payment is $294.90 for
650 payments and less than $91,687 interest, the "accel" biweekly
payment is $319.90 for 547 payments (21.04 yr) and less than $74,987
interest, and the "accel" weekly payment is $159.95 for 1093 (21.02 yr)
and less than $74,827 interest, which closely correspond to the results
of the online Canadian mortgage calculator.

Thus, the Excel formulas for Canadian "accel" schedules a

=13*pmt(rate(12/2,,-1,1+r/2), 12*term, -loan) / freq

=roundup(nper(rate(freq/2,,-1,1+r/2), p, -loan), 0)

where "r" is the annual rate, "p" is the payment (the result of the
pmt()
formula), and "term" is the nominal length (in years) of the loan based
on monthly payments. The nper() formula yields "n", i.e. the number
of payments, which I used in other formulas in my previous posting.