Pregnancy Due Date Formula Explained, With Examples
Every pregnancy due date result comes from one formula. Once you understand what goes into it, you can sanity-check any figure you are given, whether by an employer, a bank, a teacher or another website.
The formula
Due date = first day of last period + 280 days.
What each input means
- First day of last period: the value you enter in the calculator.
Example
For example, with these inputs:
- First day of last period: 1 Mar 2026
the calculator returns:
- Estimated due date: 6 Dec 2026
- End of first trimester: 6 Jun 2026
Why it matters
Health numbers are most useful when you track them consistently. A quick calculation turns everyday measurements into something you can act on, whether that is planning meals, training for a run or preparing for a clinic visit.
Singapore's tropical climate means you lose more fluid through sweat, even when you are not exercising. Thirst, urine colour and how you feel are good guides, and needs rise during outdoor activity or heat waves.
Programmes such as the National Steps Challenge and the Healthy 365 app have made tracking activity common. Turning those numbers into distance, pace or calories helps set realistic goals for events like IPPT or a 10 km run.
Research has shown that Asians tend to develop conditions such as type 2 diabetes and heart disease at lower body weights than Europeans. That is why the Health Promotion Board recommends lower BMI cut-offs for Singaporeans, with 23 marking the start of moderate risk.
Related calculations
- Ideal Weight Calculator: Gives an ideal-weight estimate and the healthy weight range for your height.
- Daily Water Intake Calculator: A rough guide to daily fluid needs in Singapore's hot, humid climate.
- Calorie Deficit Calculator: Sets a daily calorie target for steady weight loss.
- Ovulation Calculator: Estimates ovulation and the fertile window.
Use the Pregnancy Due Date Calculator to plug in your own numbers.
Run your own numbers: Pregnancy Due Date Calculator