· Built around the Pregnancy due date calculator
Photo: Daniel Reche on Pexels (free licence)
Planning a baby, or just found out one is coming? Three dates decide almost everything that follows: the days in a cycle when you are most likely to fall pregnant, the estimated due date your clinic works from, and the four months of maternity leave the Basic Conditions of Employment Act gives you. This post works all three from one real calendar using the ovulation, pregnancy due date and maternity leave calculators - and says plainly where the estimates stop.
Run your own numbers
The due date calculator takes the first day of your last period and your usual cycle length. It shows the due date, how far along you are today and your trimester.
Checked against a published example
Every calculator in this post was run on the inputs of a published example or the law itself:
- Due date: a last period on 8 May 2020 gives 12 February 2021, exactly 280 days later - the worked example in Wikipedia's Estimated date of delivery article. Our due date calculator gives 12 February 2021.
- Ovulation: about 14 days before your next period, day 14 on average in a 28-day cycle, and pregnancy possible from about five days before ovulation to one day after - Cleveland Clinic, Ovulation. Our ovulation calculator uses the same rule and window.
- Maternity leave: at least four consecutive months, starting any time from four weeks before the expected birth, and no work for six weeks after it - BCEA section 25. Our maternity leave calculator gives 1 February to 31 May 2027 for a 1 March 2027 due date, which is four months from four weeks before.
Two small fixes. The ovulation calculator labelled its date "day 14 of your cycle" when that date is day 15 (day 1 is the day your period starts) - the date was right, the label now says day 15. The due date calculator's notes said 280 days is "the same as" adding 9 months and 7 days; it is not quite - the shortcut can land up to 3 days later because months differ in length (Wikipedia's 8 May 2020 example gives 15 February by the shortcut). The calculator counts the 280 days, as clinics and most due date tools do.
Worked example 1: the fertile days
- Last period started Monday 5 October 2026, cycle 28 days, so the next period is due Monday 2 November (ovulation calculator).
- Ovulation is likely 14 days before that: Monday 19 October - cycle day 15, counting 5 October as day 1.
- The most fertile days are 14 to 20 October - the five days before ovulation, the day itself and the day after. Sperm can survive several days, so the days before count as much as the day.
- Ovulation can fall anywhere from 10 to 16 days before the next period - here 17 to 23 October.
- With a 32-day cycle the next period is 6 November and ovulation about Friday 23 October (cycle day 19), fertile 18 to 24 October.
- Irregular cycles, breastfeeding and stopping the pill all move ovulation. Ovulation tests are more exact, and this is not contraception.
Worked example 2: the due date and the milestones
- Due date = first day of the last period + 280 days (40 weeks), adjusted by the days your cycle is longer or shorter than 28 (due date calculator).
- 5 October 2026 + 280 days = Monday 12 July 2027.
- With a 32-day cycle it is Friday 16 July 2027 - 4 days later, because ovulation came 4 days later.
- Likely conception: around 19 October 2026, two weeks after the period started.
- Second trimester from 11 January 2027 (week 14), third from 19 April 2027 (week 28).
- Full term from 21 June 2027 (37 weeks); 42 weeks is 26 July. Only a few babies arrive on the due date itself.
- A first-trimester dating scan beats the calendar - if it differs, your clinic goes by the scan, so re-run the dates below from the scan date.
Photo: Leah Newhouse on Pexels (free licence)
Worked example 3: maternity leave dates
- The BCEA gives at least four consecutive months, from any day four weeks before the expected birth - earlier if a doctor or midwife certifies it is needed (maternity leave calculator).
- Due 12 July 2027, the earliest ordinary start is Monday 14 June 2027.
- Four months from 14 June runs to Wednesday 13 October 2027 - 122 days - and you are back at work on Thursday 14 October.
- Start on the due date instead and leave runs to 11 November 2027 - 123 days, because July to November has more 31-day months.
- You may not work for six weeks after the birth - to 23 August 2027 if the baby comes on the due date - unless a doctor or midwife certifies you fit.
- The four months run from the day you start, whatever day the baby actually arrives. Count working days off with the days between dates calculator.
Worked example 4: who pays
- The BCEA does not make your employer pay you on maternity leave - many contracts do, so read yours first.
- If your employer does not pay, claim from UIF: the calculator uses up to 121 days at up to 66% of pay, on pay up to the R17 712 a month ceiling (UIF benefits calculator).
- At that ceiling, 66% is at most about R11 690 a month - R17 712 x 66%. Run your own pay through the calculator.
- Plan the gap: if you earn R25 000 a month and UIF pays at most R11 690, the shortfall is about R13 310 a month for four months - check what your leave pay and savings cover.
Not verified from a primary source this run: the UIF figures (121 days, up to 66%, R17 712 a month ceiling) are the ones our UIF calculator uses; confirm your claim with the Department of Employment and Labour. A 2025 Constitutional Court judgment on parental leave changed how leave can be shared between parents - it is not modelled here, so check with your employer or HR. The BCEA text was read from the Act as published; later amendments were not checked. None of this is medical or legal advice - your clinic, midwife or doctor dates a pregnancy, and your contract may give you more than the Act.
What to do this month
Sources
Calculators used in this post
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