How to Calculate Pregnancy Due Date: A Step-by-Step Guide

Updated 5 Oct 2026 in Health & Fitness

Estimates your due date using Naegele's rule.

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.

What you need

• First day of last period

Step by step

1. Enter the first day of last period.
2. The results update as you type, or press Calculate.
3. Read the estimated due date first, then the supporting figures below it.

The formula

Due date = first day of last period + 280 days.

Worked 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

Practical tips

• Healthy 365 and wearables give useful data, but treat their calorie figures as approximate.
• Formulas give estimates for the average person; your doctor can account for your history and body composition.
• Track trends over weeks rather than reacting to a single reading.
• Measure at the same time of day, ideally in the morning, for consistent readings.

Background

Simple measurements such as weight, height and waist circumference are widely used to screen for health risks because they are cheap and easy to repeat. They are not diagnoses, but tracked over time they show whether lifestyle changes are working.

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.

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.

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.

Want to skip the arithmetic? The free Pregnancy Due Date Calculator does all of this instantly and updates as you type.

Run your own numbers: Pregnancy Due Date Calculator