Abstract: A resource planning system is disclosed for planning reserved instance server requirements for a user of cloud computing services that comprise reserved instance servers and on-demand servers accessible by the user. The system is arranged to receive historical usage data indicative of a historical usage of the cloud computing services by a user, the historical usage data covering a defined time period including a plurality of time units, and the historical usage data including information indicative of a number of server instances that were required by the user in each time unit of the time period. The system is arranged to receive cost information indicative of cost for each reserved instance server and on-demand server, and to calculate a total cost for usage of a plurality of combinations of reserved instance servers and/or on-demand servers that will satisfy the user's server requirements over the defined time period.