SQL: How to ask for multiple counts from the same table within a join

Trying to find 3 separate counts within one column of a table, each with separate WHERE clauses. I've got 2 tables in the query, so one join. Thought this looked correct but it will not run: SELECT stores.caption, COUNT ( WHEN tasks.created_at BETWEEN '2019-04-01' AND '2019-04-30' AND tasks.deleted_at IS NULL) AS TaskTotal , COUNT ( WHEN tasks.created_at BETWEEN '2019-04-01' AND '2019-04-30' AND tasks.deleted_at IS NULL AND tasks.completed_at IS NULL) AS TaskOutstanding, COUNT ( WHEN tasks.created_at BETWEEN '2019-04-01' AND '2019-04-30' AND tasks.deleted_at IS NULL AND tasks.completed_at IS NULL AND tasks.deadline < '2019-05-16') AS TaskOverdue FROM tasks FULL JOIN stores ON tasks.store_id=stores.id GROUP BY stores.caption;