Each contract has a special field "Status" which indicates whether a contract is Draft, Future, Active, Expired or Due. The status field automatically works out the status of a contract based upon the contract end date.
Fig 1 - Status field on the Contract Summary
If no date is provided in the contract end date, this indicates the contract is a "rolling contract" and the status will be set to active. A contract is consider to be "due" if the end date is within a specified amount of days of the end date. By default this is set to 30 days. This can be changed by an Administrator by changing the value "The number of days before a Contract's end date status is set to Due". See the Account Configuration article for an explanation of how to change this value.
If required you are able to override the automatic calculation of a contract's status by editing the Status field directly. Once the status field for a contract has been changed to a specific value if will remain as that value until the user moves the value back to "auto". The override can be used, for example, when a contract is passed is expiry date and so the contract is being indicated as "expired" but you may in negotiation with a supplier and service is continuing whilst the negotiation takes place.
Fig 2 -Manually changing status of a contract