Bond duration for monthly coupon
 

For some reason, Excel can only calculation duration (using the
DURATION() formula) for annual, semiannual, or quarterly coupons. It
does not work for monthly coupons. Does anyone know how to make it work
for any interval of coupons? If I can't make Excel's built-in function
to work, is there a hard formula for duration that I can enter that
would work? Cheers.

N.