Most medications follow a clock: take them at 8:00 AM, 2:00 PM, and 6:00 PM every day. But some medications work better when spaced by time — for example, "take again 4 hours after your last dose" rather than "at 4:00 PM". This is called an "After last dose" dose schedule.
PillBox automatically calculates when an "After last dose" dose is due by looking at the most recent dose you've taken of that same medication today, and adding the offset you set (for example, +4 hours). This keeps you from accidentally doubling up, and adapts to your real-world schedule.
When is it useful?
"After last dose" schedules are useful for:
- Painkillers and fever reducers — "every 4 to 6 hours as needed, but not more than 4 times a day"
- Stimulant medications — spacing out doses throughout the day
- Anti-nausea or anti-diarrhea medications — "repeat after 4 hours if needed"
- Any as-needed medication where timing matters — you want it spaced out, not rushed
Instead of remembering exactly what time you last took a dose, PillBox figures it out and updates the scheduled time automatically.
How it works
Timing follows your actual doses
An "After last dose" dose is due N hours (or minutes) after the most recent dose of that medication you've actually taken today. It's not anchored to a fixed clock time — it's anchored to your real behaviour.
Example: You have Ibuprofen with two doses set up: - Morning: 8:00 daily (clock-based) - Every 4 hours: relative to the last taken dose (after-last-dose schedule)
You take the Morning dose at 8:15. The "Every 4 hours" dose is now due at 12:15 (8:15 + 4 hours), not 4:00 PM.
Later, you take another dose at 12:30. Now the next "Every 4 hours" dose slides to 16:30 — it's always 4 hours after your last actual dose. This keeps you from double-dosing if you took something earlier than expected.
Skip doesn't count; only taken doses count
If you skip a dose, it doesn't move your relative schedules. Only taking a dose updates them.
Example: Same Ibuprofen setup. You take the 8:00 Morning dose at 8:20. The relative dose is now due at 12:20. Later, you skip a clock-based dose at 14:00. The relative dose is still due at 12:20 — skipping didn't change it.
Provisional times
Before you've taken any dose of a medication today, "After last dose" doses show as provisional times — they're shown in the Today view but don't notify you yet. The provisional time is an estimate based on the earliest dose still scheduled for that medication today — its clock time plus your offset.
Once you take your first dose of the day, the relative schedule starts counting from that actual time — and it keeps updating: every later dose you take moves it again.
Example: You have an Ibuprofen medication with a morning clock dose at 8:00 and a relative dose "every 4 hours". It's 7:00 AM and you haven't taken anything yet. The relative dose shows provisionally at 12:00 (8:00 + 4 hours), but it won't notify — it's just a forecast. Once you take the 8:00 dose at, say, 8:20, the relative dose updates to 12:20 — and if you take another dose later, it moves again.
Waiting for as-needed doses
If a medication is as-needed only (no scheduled doses at all, just "as needed"), and you haven't logged a dose yet today, a relative schedule can't calculate a time — there's nothing to count from. In this case, the dose appears as waiting — a quiet placeholder with no notification. Once you log the first as-needed dose, the relative schedule springs to life and counts from that time.
When a medication has only relative doses
If a medication has only relative doses and no regular scheduled doses, PillBox shows a warning. Relative doses need something to anchor to — at least one regular dose or an as-needed dose that you can log. This prevents a medication with no way to get started.
What if you take nothing all day?
If it's evening and you haven't taken a dose of that medication yet, the relative dose can't fire — it has no anchor. Instead, PillBox marks it as missed at the time when your reminder would normally stop (set in Settings under Stop & mark missed after). This is honest: a dose that can't calculate a time can't be taken, so it gets marked as missed when it's too late in the day to take it.
Setting up an "After last dose" dose
- Open a medication or tap + Add Dose.
- In the Type row, choose After last dose.
- Set the Offset — how long after your last taken dose (15 minutes to 24 hours in steps: 15m, 30m, 45m, 1h, 1h30, 2h, 2h30, 3h, 4h, 5h, 6h, 8h, 12h, 18h, 24h).
- Set the Strength and Quantity the same way as any other dose.
- Turn reminders on or off as usual.
- Tap Done.
Note: "24 hours" is a special offset. It acts like every 24 hours (23 hours 59 minutes, technically) — close enough to a calendar day that it breaks the tie with the next day's doses and keeps your doses aligned cleanly. Displayed as "24h" for simplicity.
Same-medication rule
An "After last dose" dose only counts doses of the same medication. A relative Ibuprofen dose looks at Ibuprofen takes only — it doesn't care when you took Paracetamol or any other medication.
Offset offsets, and chains
If you set up multiple "After last dose" doses with the same offset — for example, two "every 2 hours" doses — they create a chain. The first one is due 2 hours after your last take, the second is due 4 hours after it, and so on.
The order in which you add the doses sets the chain order. The Today view sorts them by calculated time, but they stay chained for display and ordering purposes.