Pregnancy Calculator
Overview
This calculator helps you estimate your due date, current gestational age, and the key checkpoints that typically appear on the Finnish maternity-care timeline. It mirrors the three approaches that midwives use: counting from the first day of your last menstrual period, counting from a known conception date, and recalculating the schedule with an ultrasound measurement (weeks + extra days). The goal is to give you an always up-to-date roadmap that adjusts instantly when you receive new medical information.
Inputs & Usage
Start by choosing the calculation method. Last menstrual period is the quickest option for regular cycles: enter the first day of bleeding and your usual cycle length so the calculator can shift the ovulation window if needed. Conception date is ideal for assisted reproduction or other scenarios where fertilisation is known precisely. Ultrasound measurement expects the date of the scan and the gestational age that the sonographer wrote down (for example 12+3). You can jump between methods at any time—the tool reverse-engineers the missing dates and keeps the milestone list in sync.
How It Works
The underlying model assumes a 40-week (280-day) pregnancy. LMP-based calculations add or subtract the difference between your cycle length and the standard 28 days before counting forward. Conception-based timelines add 266 days to approximate 38 gestational weeks from fertilisation. Ultrasound calculations subtract the measured weeks+days from the scan date to recover the adjusted pregnancy start and then move forward to the due date. The output includes: revised LMP, estimated conception, due date, gestational age, fetal age (two weeks less) and a curated milestone list such as the combined first-trimester screening, anatomy scan, glucose screening and the earliest parental-leave window.
Interpretation
The summary cards show due date, weeks+days, current trimester, fetal age and progress expressed as a percentage of 40 weeks. Use the percentage and trimester label to discuss lifestyle adjustments or workplace notifications. The milestone list highlights whether each event is already completed, happening soon or still far away. Values update in real time, so you can rerun the tool after every appointment.
Example
Imagine the last menstrual period started on 12 September with a 26-day cycle. Because ovulation usually happens two days earlier than the 28-day reference, the calculator shifts the due date from 19 June to 17 June. Entering a dating ultrasound performed on 5 December that measured 13+0 weeks yields the same adjusted due date, proving that both methods agree.
Limitations
The calculator does not cover multiple pregnancies, medically induced deliveries, or region-specific care protocols. Official maternity-leave eligibility and screening schedules are defined by healthcare professionals and local legislation. Treat every output as educational information and confirm timing decisions with your care team.