Using Excel 2010

The known values are:
1. the current modal payment amounts
2. the annuity interest rate
3. the indexing rate (only one indexing rate, which is static for the life, but indexing of future payments,takes place each anniversary)
4. the payment mode (monthly, quarterly, semi-annual, or annual).

As a result the nominal annual interest rate needs to be adjusted to reflect the mode.
The indexing of future payments seems to be the tricky part to this.

Thanks in advance