Normally, when you calculate a fix-term mortgage with any payment schedule, be it monthly, bi-weekly, or weekly, the goal is to pay off the loan at the end of the term. The more frequent you pay, the less interest will accrue, and you save money on the interest. Take a 15-year, $200,000 loan with an interest rate of 7.5% for example:

	Each Payment	Total Payments	Total Interest
Monthly	$1,841.03	$331,384.92	$131,384.92
Bi-Weekly	$848.30	$330,837.55	$130,837.55

The accelerated bi-weekly payment is, take the monthly payment above (as if you were to pay off the loan in 15 years) and divide it by 2, enforcing a fictitious 28-day month.

Notice that this amount ($920.51) is significantly higher than the normal bi-weekly payment ($848.30), resulting in the loan being paid off much earlier than the original term of 15 years, therefore the acceleration.

	Each Payment	Total Payments	Payoff Time
Bi-Weekly	$848.30	$330,837.55	15 years
Accelerated Bi-Weekly	$920.51	$311,242.27	13 years

Accelerated weekly is essentially the same as accelerated bi-weekly, except that the payment amount is calculated by dividing the monthly payment by 4, instead of 2.