Difference between Last Modified Date and Last Activity Date
Last Modified is the date and time stamp for changes (for example, changes to a phone number or an address) made to an individual record. This also shows the User who made the change.
Last Activity shows when someone in your Organization last did something related to the record. It represents one of the following:
- The latest Due Date of the closed tasks on a record.
- The latest Date of events on a record.
For example: If you have multiple Activities on a record, the Last Activity would show the Due Date which is farthest of all. So, if the Due Date on all Activities are 1/01/2015, 2/01/2015, 3/01/2015, the Last Activity would show "3/01/2015" on the report and would take this date into consideration when filtering the List Views. In List Views and Reports, the Last Activity is labeled "Last Activity." Last Activity is not available to add to the Page Layout.
Note: A single Task may be related to more than one record. For example, a Task may be related to both an Account and an Opportunity, or a Task may be related to both a Contact and a Case. To make sure that records actually reflect last activities, use the "Related To" field whenever you log a call, create a Task, send an email, or schedule an Event.
Calculate Last Activity Date
Each Activity record has an "account_id" field that is different from the "what_id" and "who_id" fields. However, the value for the "account_id" field is calculated by introspecting the who and the what, with the what taking precedence.
Here are the rules:
- If the What is an account, the account_id is that account.
- If the What is an opportunity, the account_id is the account associated with that opportunity.
- If the What is a contract, the account_id is the account associated with that contract.
- If the What is a Custom object that is parented under an account, the account_id is the account associated with that custom object.
If the "account_id" cannot be derived from the What using the above, then we look to the Who. If the Who happens to be a contact with an associated account, then the "account_id" is the account associated with that Contact.
Once the "account_id" value is determined (it can be null, if none of the above applies), and if the Activity is not deleted, the Activity becomes a candidate for Last Activity Date calculations for the associated Account. So it can be seen that for LAD on an Account, we utilize not just those activities that have the Account as the What but also Activities that effectively roll-up to the Account via the Contract, Custom object, Opportunity and Contact.
In case you use Shared Activities, please review their behaviour in regards with Last Activity Date: