BabyBump's default setting shows your Current Day which counts days of the week from Day 1 to Day 7. So you will be on Day 7 on the last day of your week and on Day 1 on the first day of the next week. For example, if today is Week 17, Day 7, then tomorrow will be Week 18, Day 1.
You can also show days by Days Past (0 Days to 6 Days). This will appear as Week XX, 2 Days past.
You may also choose to show each week by Complete Weeks or Current Week.