Within Basecamp, each person has a schedule that will populate all tasks and events assigned to them. To have your Basecamp assignments appear on your Outlook Calendar, follow the steps below:
In Basecamp, select "my stuff" and then "my schedule"
Select "Add this schedule to..."
Select Outlook
Select Open "Calendar.app"
Copy the Basecamp link (you can cancel and close the calendar app.)
Next head over to outlook on the web to add this calendar, direct link: https://outlook.cloud.microsoft/calendar/addcalendar - Then select "Subscribe from web" and paste the calendar link and fill out additional details like calendar name, color, and icon. Once done click import:
Your Basecamp schedule will now appear in your outlook. Now all tasks and events you are assigned in Basecamp will appear in your Outlook Calendar, and it will stay up to date as changes happen in Basecamp.
Some last notes and other use cases.
These steps can also be repeated for project calendars to make events scheduled in Basecamp appear in Outlook. For example lets say you are working on upcoming life groups events using Basecamp, you need a way to share this calendar to your staff but not everyone is in the lifegroups project - But if you share the calendar link from step 5 others can import that schedule directly into their outlook calendars. This works even for folks who don't have Basecamp!
Keep in mind Basecamp tasks and events can only be edited in Basecamp.
Keep in mind that each calendar in each project has its own calendar, but that your schedule is an aggregate of all tasks and events assigned to you - you probably don't want to share the link to your schedule with others since they have their own schedule.
IT recommends everyone using Basecamp add their schedule to their Outlook - and then separately add individual projects they are responsible for.