BF is short for beräknad förlossning, the Swedish term for your estimated due date, in other words the date your baby is expected to arrive. You work it out from the first day of your last period. Add 280 days, or 40 weeks, and you have a preliminary due date. Then the midwife fine-tunes the date at the ultrasound. That's how simple, and how uncertain, it is. Here we go through how to count, why the date rarely lands on the exact day, and what's nice to have ready beforehand.
How to work out your due date yourself
Pregnancy isn't counted from conception but from the first day of your last period. That's why you're "in week 2 of pregnancy" before the egg has even been fertilised. A little odd, but practical, since most people know when their period came and few know exactly when conception happened.
The classic trick, which midwives have used for ages, goes like this:
- Take the first day of your last period.
- Add 7 days.
- Count back 3 months.
- Add one year.
Example: Your last period started on 1 March. Add 7 days: 8 March. Count back three months: 8 December. That's roughly where your due date lands.
Would you rather count straight through? Add 280 days to the first day of your period. The two methods can differ by a day or so depending on how many days the months have, so treat the result as a guide, not a booking.
If your cycle isn't 28 days
The formula assumes a 28-day cycle with ovulation around day 14. If your cycle is longer, ovulation usually happens later, and your real due date will be a little later than the formula says. Shorter cycle, the opposite. If you're unsure when your period came, or your cycle is irregular, that's completely fine. The ultrasound sorts it out.
The ultrasound sets the final date
At the ultrasound, the midwife or doctor measures the fetus and compares its size with how far along the pregnancy is expected to be. Based on that, the due date may be moved a few days forward or back. That's the date that counts from then on, in your records, at the antenatal clinic and in your own calendar. So go ahead and count at home, but write it in pencil.
How reliable is a due date, really?
Not very, if we're honest. Few babies are born exactly on their due date. The date is the middle of a range, not a promise. A pregnancy counts as full term from week 37 through week 42, and babies are born healthy and happy across that whole range. So when someone asks "when are you due?" you can calmly answer "December, sometime".
This is worth remembering when you plan. Your baby could arrive three weeks before the due date, or a couple of weeks after. So anything that needs to be ready should be ready a good while before the date, not the day before.
Which week am I in now?
Count the number of weeks from the first day of your last period until today. If 20 full weeks and 3 days have passed, you're in week 21 (often written as "20+3"). So week 1 starts on the first day of your period, and the due date falls at 40+0. It's easy to mix up "week 21" with "21 weeks pregnant", which is why midwives usually say weeks plus days to avoid confusion.
What do you sort out before the due date? A calm checklist
You don't need everything. Babies have surprisingly few demands. But a few things are nice to have in place a few weeks before the date, so you're not rushing around with your bump in the way.
- Car seat, fitted and tested, so you don't end up reading the manual in the maternity ward car park.
- Clothes in the smallest sizes, washed and ready.
- Somewhere to sleep for your baby, whether it's a baby nest, cradle or cot.
- The hospital bag, packed well ahead of time with what you need for you and for your baby.
- Diapers in newborn size, ideally in two sizes, since you don't know how big your baby will be.
- Wipes that are kind to new, thin skin.
The diapers: keep two sizes at home
This is where our own experience comes in. Newborns vary a lot in weight, and the weight ranges on diapers are always an indication. That's why we recommend having both The Mini (3 to 5 kg) and The Newborn (4 to 7 kg) at home before your due date. Many babies use The Mini for the first few weeks and then move on to The Newborn. That way you can test which one fits best, without having to order in a panic.
Want to feel the diaper before you buy a whole box? Order a sample kit of open diapers, three diapers in the size you choose. Small, simple and easy to tuck into your hospital bag.
Why bamboo is such a good fit from day one
New skin is thin and easily irritated. Our open diapers have 100% bamboo fiber against the skin, soft, breathable and without lotions or perfumes. The bamboo fibers wick moisture away fast and stay dry for up to 12 hours, which means fewer changes in the middle of the night, at least for diaper reasons. And significantly less plastic than conventional diapers, for the planet your baby is about to discover.
Parents who've tried them put it like this: "These are the only diapers that don't give my daughter a rash. They're so soft and comfortable against the skin, it really feels like the material breathes." And if the diaper does cause a rash, you get your money back. That's our promise.
Start your subscription before your due date, pause if baby is running late
Since a due date is a window rather than a date, it's smart to have diapers at home well in advance. With a subscription for open diapers you get a full month of diapers delivered to your door, with no shipping cost. If baby arrives later than expected, you pause. If baby outgrows the size, you switch. And if everything feels like too much that first week, at least you won't have to think about diapers.
Need wipes at the same time? The Bamboo Water Wipe, 4 packs, is available on a monthly subscription. Gentle on skin, and delivered to your door.
Frequently asked questions about your due date
Is the due date counted from conception or from your period?
From the first day of your last period. Conception normally happens about two weeks later, but the whole pregnancy, including weeks 1 and 2, is counted from your period.
Can the due date change during pregnancy?
Yes, usually after the ultrasound. Measuring the fetus can shift the date by a few days. After that, the due date usually stays fixed.
What happens if the baby doesn't arrive on the due date?
Completely normal. Most babies don't arrive on the day. Your maternity care team follows you and your baby and will tell you what happens if things run late.
When should the diapers be at home?
A few weeks before your due date, in two sizes. Your baby may arrive earlier than expected, and then it's nice if all you have to do is open a box.
Calculate your due date, put it in the calendar, and then stay calm. The date is an estimate. Being ready in good time is what actually brings peace of mind. Try Bammies now, and that part is sorted.
