# Time of Supply under the HAM Model
The Hybrid Annuity Model (HAM) is used for road construction contracts awarded by NHAI. A concessionaire builds the road, NHAI pays part of the cost during construction and the balance as annuities (with interest) over the operation period along with O&M payments.
## Classification
The activity is treated as a continuous supply of service because the contract obligates the supplier to provide services on a recurring/continuing basis (construction + O&M) over a long period under a single agreement.
## Time of Supply
For a continuous supply of service of this nature, the time of supply is linked to the date of completion of an event as specified in the contract.
- The HAM contract typically sets out milestone events (e.g., completion of a stretch, achievement of a project deliverable, scheduled annuity due dates).
- GST liability arises on the date of completion of each such event.
## Why a circular was needed
HAM contracts mix construction, financing (interest on deferred annuities), and O&M into one continuous stream. The CBIC circular clarified that:
1. The supply is a continuous supply of service.
2. ToS is the date of completion of the event milestones identified in the contract.
3. Interest component on deferred annuity is also part of taxable value.
## Quick recall
- HAM = NHAI + concessionaire + annuity-based payments.
- Continuous supply of service → ToS = date of event completion per contract.