This second pregnancy due date calculator estimates the due date for a subsequent pregnancy from the first day of the last menstrual period (LMP + 280 days) and shows the age gap between the first and second child at the projected birth date. It displays current gestational age in weeks and days, trimester identification, and WHO recommendations on ideal pregnancy spacing (18–24 months between delivery and next conception).
Second Pregnancy Due Date Calculator
Calculate your due date for a subsequent pregnancy, with age gap from your first child.
How the Second Pregnancy Due Date Calculator Works
This calculator estimates your due date for a subsequent pregnancy using the standard last-menstrual-period method, and — if you enter it — works out the age gap between your first child and this new baby at the projected birth date.
Formula: Estimated due date = first day of last menstrual period (LMP) + 280 days (40 weeks), the same standard convention used for a first pregnancy. Current gestational age is calculated as the number of days between your LMP and today, divided into weeks and remaining days, with under 13 weeks labeled the first trimester, 13-26 weeks the second, and 27 weeks or more the third. If you also enter your first child’s birthday, the age gap at the new baby’s due date = (due date − first child’s birthday) in days, converted to years and months (years = whole 365.25-day years, months = the remaining days divided by 30.44).
- First Day of Last Menstrual Period — the start date used to project your due date and gestational age
- First Child’s Birthday — optional; used only to calculate the projected age gap between your children
Example Scenarios
| Last Menstrual Period | First Child’s Birthday | Estimated Due Date | Age Gap at Birth |
|---|---|---|---|
| Jan 1, 2026 | Jun 15, 2023 | Oct 8, 2026 | 3 years, 3 months |
| Mar 1, 2026 | Sep 1, 2024 | Dec 6, 2026 | 2 years, 3 months |
| May 10, 2026 | Aug 1, 2024 | Feb 14, 2027 | 2 years, 6 months |
| Jul 4, 2026 | Mar 15, 2025 | Apr 10, 2027 | 2 years, 0 months |
| Sep 20, 2026 | Sep 20, 2021 | Jun 27, 2027 | 5 years, 9 months |
How Accurate Is a Second Pregnancy Due Date Calculator?
A second pregnancy due date calculator uses the same LMP-plus-280-days rule as for a first baby, so it assumes a regular cycle of about 28 days with ovulation around day 14.
- Cycles often change after a birth. If your periods have not settled, the second pregnancy due date calculator may be off by a week or more.
- Some people conceive before their first period returns, leaving no LMP to enter. An early dating ultrasound is then the usual way to set the date.
Few babies arrive on the exact day; most come within a couple of weeks either side. Use the second pregnancy due date calculator for planning leave, care for your older child and family help, not as a fixed deadline.
Pregnancy is not automatically shorter the second time, though labour is often quicker, and a second pregnancy due date calculator cannot predict either. Mention any complications from your first pregnancy to your midwife early. The Naegele’s rule article on Wikipedia explains the method behind the second pregnancy due date calculator, and your care team can confirm or adjust the date.
Second Pregnancy Due Date Calculator FAQ
How is the due date calculated from my last menstrual period?
The calculator adds 280 days (40 weeks) to the first day of your last menstrual period, the same standard convention used for a first pregnancy or any LMP-based due-date estimate. It’s a general estimate, not a diagnosis of when you’ll actually give birth.What if I don’t know my first child’s birthday or don’t want an age gap shown?
Just leave that field blank — the calculator still returns your estimated due date and current gestational age without it. The age-gap field only appears once you enter a birthday.Why might my actual pregnancy dating differ from this LMP-based estimate?
LMP dating assumes a fairly typical cycle length and ovulation timing, which varies between people and even between cycles. A dating ultrasound from your provider is generally considered more precise and should take priority over this estimate.What is considered a healthy amount of spacing between pregnancies?
Public health guidance, including from the World Health Organization, has generally suggested spacing of around 18 to 24 months between a birth and the next conception where possible. This is general population-level guidance, not a personal recommendation — your own provider can advise on spacing for your specific situation.How is the age gap between my children calculated?
It’s the difference between your projected due date and your first child’s birthday, converted from days into years and months. It’s an estimate based on your due date, so if your baby arrives earlier or later than projected, the actual gap may shift slightly.Does this calculator account for irregular cycles or a different cycle length?
No — it uses the standard fixed 280-day estimate from LMP, the same method most basic due-date calculators use, and doesn’t adjust for irregular or unusually long or short cycles. If your cycles are irregular, a dating ultrasound will give a more reliable estimate than this calculation alone.Related Calculators
If you’re timing this pregnancy or tracking your cycle beforehand, the ovulation calculator can help pin down a likely conception window, while the pregnancy week calculator is useful for tracking weekly progress once you’re expecting. If you’re still in the recovery window from your last birth, the postpartum recovery timeline covers what’s typical at each stage.