General advice is to have a hospital bag packed by about 36 weeks. The labor calculator provides a more specific date: the 10% date, the day by which there is a one-in-ten chance that labor has already begun. For a first pregnancy with no adjusting factors, that date is about 38 weeks 6 days when calculated at 36 weeks.
Packing by 36 weeks leaves a margin of nearly three weeks before it.
The margin is the point. A packing deadline should fall before the date by which labor has become reasonably likely, not on it.
What the 10% date is
The calculator's forecast is a probability distribution over the remaining days of the pregnancy. The 10% date is the day on which the cumulative probability from today reaches 10%. It moves later as the pregnancy continues, because days that pass without labor are removed from the distribution and the remaining probability is rescaled.
In the baseline model for a first pregnancy, the 10% date is about 38 weeks 5 days when calculated at 34 weeks and 38 weeks 6 days when calculated at 36 weeks. At 39 weeks 0 days it is 39 weeks 4 days, and at 40 weeks 0 days it is 40 weeks 2 days. The date holds nearly still through late pregnancy and then approaches quickly, which is why a packing decision made at 34 to 36 weeks is stable.
Before 37 weeks
About 5% of singleton pregnancies begin labor spontaneously before 37 weeks, based on the 4.5% rate reported by Gyamfi-Bannerman and Ananth (2014). From 34 weeks 0 days, the baseline model gives about a 3% chance of labor before 37 weeks. From 36 weeks, it gives about 1%. A previous spontaneous preterm birth raises these figures, and the calculator's result page shows the before-37-weeks chance for the answers entered.
A bag packed by 36 weeks therefore covers all but about 1% of first pregnancies, and a bag packed by 34 weeks covers all but about 3%. For anyone whose calculator result shows a raised before-37-weeks chance, or whose care team has said so, packing earlier follows from the same arithmetic.
A timeline
The steps below are ordered by how much lead time each needs, not by a fixed week. The dates come from the calculator's result for the answers entered.
- By the 10% date less three weeks, or by 34 weeks, whichever is earlier: ask the birth location what it provides, confirm the car seat is installed and checked, and decide where the bag will be kept. These steps depend on other people and are the ones most often left late.
- By the 10% date less two weeks: pack the documents, the parent's items, and the baby's going-home clothes in two sizes. Set aside a labeled refill bag at home.
- By the 10% date less one week: add the support person's items, charge a battery pack, and save the route and parking instructions where a driver can find them.
- Ongoing: keep the grab-before-leaving list visible. Medicines, refrigerated snacks, and the wallet, keys and phone cannot be packed in advance.
For a first pregnancy at baseline, step 1 lands at about 34 weeks, step 2 at about 36 weeks 6 days, and step 3 at about 37 weeks 6 days.
How the tools connect
The hospital bag checklist works without a due date and covers the items. The Labor-Ready Plan is a paid feature of the labor calculator. It takes the forecast and assigns a date to each preparation task using a readiness setting. The default sets the ready-by date at the 10% date, and the user can choose an earlier one. Task dates move with the forecast as it is recalculated, and custom dates such as a trip or a family arrival can be added and compared with the weekly probabilities.
Neither tool predicts when labor will begin. The median of the baseline forecast is about day 284 for a first pregnancy, following Smith (2001), and half of first pregnancies continue past it. A bag packed at the 10% date less two weeks will, for most people, wait in a closet for a month.