A zero-coupon bond has negative amortization: no interest payments are made (the principal accumulates) until maturity.

The principal at year t is:

Pt=Pt-1(1+r)
r
Specified interest rate or yield
P
Principal value at a given point
The tax rate on a such a bond is imputed:
r=(PT/P0)1/T-1
r
Tax rate
T
Time of maturity
P
Principal value at a given point
Thus one pays Pt-1r at time t.