Forum Discussion
Cost increases when selecting Amortised cost in cost analysis
Hi, this seems like a bug. When i select Amortized cost in Cost analysis, our monthly cost jumps from $25,664.54 to $76,315.83.
The resource that causes the jump is a Reservation for a D4asv5 virtual machine. It jumps to $3,120.09 per day.
Can someone please try it their side.
2 Replies
Seems it is an expected behavior tied to how reservations are accounted for, the jump reflects how Azure spreads reservation costs over time for reporting accuracy. It does not mean you are being overcharged but simply shows the true daily cost allocation of your prepaid reservation:
https://learn.microsoft.com/en-us/azure/cost-management-billing/reservations/view-amortized-costs
https://learn.microsoft.com/en-us/azure/cost-management-billing/reservations/reservation-utilization
https://learn.microsoft.com/en-us/azure/cost-management-billing/costs/quick-acm-cost-analysis
That jump can be expected when switching metrics, because Actual cost and Amortized cost answer different questions. Actual cost shows reservation purchases when billed; amortized cost spreads the reservation price across its term and assigns the daily cost to covered resources. A reservation purchased earlier can therefore make a later month look much higher in amortized view without creating a new charge. Keep the same scope and date range, then filter Pricing model to Reservation and use Daily granularity. Group by Reservation name, then Resource. Check Charge type for UnusedReservation, which identifies paid capacity not used. Compare the result with Actual cost and the invoice; do not add both totals together. If the D4asv5 reservation still shows about $3,120 daily, verify its term, quantity, payment schedule, scope, and utilization. If those do not explain it, export amortized cost details and open a Cost Management support request with the reservation ID.
