I'm not understanding how the partial upfront work for ec2 reserved instances. I'm trying to calculate how much the instance will cost on one year.

If, for example, I add an m4.xlarge instance reserved for one year with partial upfront on AWS Calculator it returns the following information on the estimate tab:

Amazon EC2 Service (US-East): 702.02

- Compute: 54.02

- Reserved Instances (One Time Fee): 648.00

Total One-Time Payment: 648.00

Total Monthly Payment: 54.02

My doubt is if the monthly payment is included in the first month.

Should I calculate the cost of an entire year as 648 + **12** * 54.02?
Or the cost is 648 + **11** * 54.02?

Thanks