Extra Payments go toward principal or interest in template?

[Lindsay]

I just downloaded the excel template "Loan Calculator with extra payments"
and was wondering if the extra payments went toward interest or principal?

 

[Debra Dalgleish]

Using the template here:

http://office.microsoft.com/en-ca/templates/TC010755921033.aspx

If I type an extra payment amount in cell E18, it's added to the
principal amount in cell G18