Pregnancy Due Date Calculator

Estimate your baby's due date based on the first day of your last menstrual period.

days (21–35)

Your estimated due date

Enter the first day of your last period and we'll estimate your due date and pregnancy timeline.

How it works

Your estimated due date is calculated from the first day of your last menstrual period. Pregnancy is conventionally measured from that date — not from conception — because most people know when their last period started but rarely know the exact day of ovulation.

How the calculation works

We use Naegele's Rule, which has been the standard method since the 19th century: add 280 days (40 weeks) to the first day of your last menstrual period. The rule assumes a 28-day cycle with ovulation on day 14. If your cycle is longer or shorter, ovulation shifts by the same number of days, so we adjust the due date to match.

Once we have the due date, we work backwards from today to estimate your gestational age in weeks and days, and place you in the correct trimester.

A worked example

If your last period began on 1 March and you have a typical 28-day cycle, your estimated due date is 1 March + 280 days = 6 December. If your cycle is 32 days, ovulation is four days later, so the due date shifts to 10 December.

Why this matters

A reliable due date drives almost every practical decision of pregnancy: when to book your dating and anomaly scans, when to start your maternity leave, when to pack a hospital bag, when to start your antenatal classes, and when to call the midwife if labour hasn't started. It also matters medically — gestational age determines screening eligibility, growth assessments, and the timing of any induction discussion.

Pregnancy milestones to expect

  • Weeks 8–10: first midwife appointment, often called the "booking" appointment.
  • Weeks 11–14: dating scan, which confirms or revises the due date.
  • Weeks 18–21: 20-week anomaly scan.
  • Week 28: third-trimester begins; blood tests and anti-D injection (if rhesus negative).
  • Weeks 36–40: presentation check, labour planning and birth preparation.
  • Week 40: estimated due date — but anywhere from 37 to 42 weeks is considered full term.

Common mistakes

  • Using the date of conception instead of the first day of your last period — that gives a date about two weeks early.
  • Assuming the calculator's date is fixed. The 12-week scan often revises it by a few days.
  • Treating the due date as a hard deadline. Only about 1 in 20 babies arrive on it.
  • Ignoring cycle length. A 35-day cycle shifts the due date by a week compared to a 28-day cycle.

This calculator is an estimate and not a substitute for advice from your midwife or GP. For UK maternity care, the NHS has detailed pregnancy week-by-week guides.

Related tools: BMI Calculator · Calorie Needs Calculator · Daily Water Intake Calculator

Frequently asked

Complete Guide

The Everyday Guide to Better Health: Small Habits That Make a Big Difference

Lasting health isn't built on dramatic overhauls. It's built on small, repeatable habits that fit into a busy life — and a kinder way of thinking about progress.

Reviewed by the Calcaroo Editorial TeamEstimated reading time: 11 minutes
The Everyday Guide to Better Health: Small Habits That Make a Big Difference

Quick takeaways

  • Consistency beats intensity: a daily 15-minute walk does more than an occasional five-mile run.
  • Start smaller than feels impressive: one habit at a time, until it's automatic.
  • Numbers are feedback, not verdicts: BMI, calories and hydration targets are dashboards, not scorecards.
  • Four foundations: nutrition, movement, sleep and mental wellbeing support everything else.
  • Modern life is genuinely harder: you haven't failed — the environment has changed.

If you have ever caught yourself wondering how life got so busy, or why looking after your health feels rather more complicated than it used to, you are certainly not alone.

Think back over the last few generations. Without making a conscious effort to join a gym or follow a strict wellness plan, our parents and grandparents naturally lived at a slightly slower pace. They walked more out of necessity, cooked from scratch because convenience foods were rare, pottered outdoors, and enjoyed regular rhythms of rest. They weren't striving for "optimal wellness" — it was simply how everyday life worked.

Today, many of us spend hours sitting at desks or looking at screens, rely on quick convenience foods to get through packed schedules, and are constantly surrounded by advertising encouraging us to consume more. This isn't about casting blame on modern life; it brings wonderful opportunities, flexibility and connectivity. But our environment has changed dramatically, and the world around us isn't always designed to make healthy choices easy.

Here is the most reassuring thought you can take away today: small improvements made consistently are far more powerful than chasing perfection.

Better health starts with small habits

When we decide to take better care of ourselves, it is very tempting to swing straight into an all-or-nothing mindset. New workout gear, cupboards cleared overnight, a vow to wake at 5:00 AM. More often than not, that enthusiasm burns bright for a week or two before crashing into exhaustion — because dramatic overhauls rarely survive a stressful week at work, a sick child, or a rainy Tuesday evening.

Lasting health is built on micro-habits: tiny, manageable changes that fit so seamlessly into your day that you barely have to think about them.

  • Consistency beats intensity: a brisk 15-minute walk every single day is infinitely better for your body and mind than running five miles once a month until you drop.
  • Embrace gradual progress: pick one small thing — a glass of water first thing, or an extra handful of vegetables at dinner — and let it become second nature before adding another.
  • Ditch all-or-nothing thinking: missing a workout or eating a slice of cake does not ruin anything. The secret is simply returning to your normal routine at the very next opportunity.

Understanding your numbers

When people start out towards a healthier lifestyle, they often look for benchmarks. Understanding your personal metrics can be genuinely helpful, provided you keep things in perspective. Numbers never define a person, nor measure your worth, happiness or character — but they can act like a dashboard in a car, giving useful feedback so you know how the engine is running.

To help you understand your baseline without stress, you can explore several free everyday tools on Calcaroo:

  • BMI Calculator: a simple way to check your height-to-weight ratio as a general indicator of healthy weight ranges.
  • Calorie Needs Calculator: helps you understand your estimated daily energy expenditure based on your activity levels.
  • Daily Water Intake Calculator: gives you a personalised hydration target depending on your body size and daily movement.
  • BMR Calculator: estimates the baseline energy your body burns just keeping you alive at rest.
  • Body Fat Calculator: offers further insight into body composition beyond simple weight scales.
  • Ideal Weight Calculator: shows a healthy weight *range* for your height rather than a single target number.

Remember, no single number tells the whole story. Your health is a combination of how you feel, how well you sleep, your energy levels and your overall vitality. Use these tools as friendly guides rather than strict scorecards.

The four foundations of everyday health

Rather than worrying about complicated wellness trends, it helps to focus on four fundamental pillars that support everyday wellbeing.

1. Nutrition: nourishing without restriction. Good nutrition is not about deprivation, guilt or restrictive diet fads. It is simply about giving your body the fuel it thrives on.

  • Cook at home more often: even two or three more meals from scratch each week puts you back in control of what goes on your plate.
  • Focus on whole foods: plenty of colourful vegetables, fruit, wholegrains, beans, pulses and lean proteins.
  • Practise portion awareness: eat when you are hungry and stop when you are comfortably satisfied.
  • Enjoy treats without guilt: a piece of chocolate or a weekend pastry eaten with genuine enjoyment has a place in any balanced life.

2. Movement: finding ways to move naturally. Exercise does not have to mean punishing yourself in a crowded gym for an hour. Natural movement counts just as much.

  • Walking: a brisk daily walk is one of the most underrated forms of cardiovascular and mental health medicine available.
  • Everyday activity: gardening, cycling to the shops, playing in the park, or doing housework all contribute.
  • Strength: bodyweight movements, carrying shopping bags, or gentle yoga help maintain muscle tone and bone density as we age.

The golden rule is simple: all movement counts. Find things you genuinely enjoy, because you are far more likely to stick with them.

3. Sleep: the ultimate recharge. It is easy to sacrifice sleep when life gets busy, but sleep is the foundation everything else rests on. It directly affects your energy, mood, concentration, immune system and even appetite regulation.

  • Keep roughly consistent bedtimes and wake-up times, even at weekends.
  • Wind down in the evening by reducing screen time for an hour before bed.
  • Keep your bedroom cool, dark and quiet.

4. Mental wellbeing: finding your balance. Physical and mental health are deeply connected. Chronic stress, loneliness and mental fatigue eventually show up in the body.

  • Make time for small moments of calm — reading, music, or tending to houseplants.
  • Spend a few minutes outside every day to soak in natural daylight.
  • Nurture social connections by catching up with a friend or checking in on a neighbour.

Why healthy choices feel harder today

If healthy living sometimes feels harder than it "should", that is not because people have become lazy, weak or less disciplined. The modern environment simply asks more of us. We are trying to care for our bodies in a world that often makes the less healthy option the easiest, quickest and most heavily promoted one.

Busy lifestyles are a major part of the picture. Many people balance work, commuting, childcare, caring responsibilities and endless admin. Even working from home isn't necessarily more restful — it can blur the boundaries between work and rest, reduce natural movement between meetings, and make it far easier to snack simply because the kitchen is always nearby.

Desk-based work brings its own challenge. Large parts of the day can pass with barely any movement at all. Add constant access to food, oversized portions, ultra-processed snacks engineered to be hard to stop eating, and sugary drinks that deliver a great deal of energy without much fullness, and it becomes easier to see why so many people feel as though they are swimming against the tide.

Modern life also places persuasive advertising almost everywhere. Food marketing doesn't merely inform; it nudges, tempts and normalises frequent snacking and oversized indulgence. Late-night screen time pushes bedtimes later and leaves us more tired the next day, which makes nourishing food and movement feel harder again. Stress ties all of this together.

Living in a modern world

Struggling to maintain healthy habits in today's world is not a personal failure. We live in an environment overflowing with convenience. Supermarket shelves are packed with ultra-processed foods designed to be hyper-palatable, restaurant portions have crept steadily upwards, and our phones are engineered to keep us scrolling late into the evening.

When modern life encourages us to sit more, eat more convenience food and stay constantly connected, making mindful choices requires conscious effort. Be gentle with yourself. Recognising these outside pressures helps shift the narrative from personal failure to practical problem-solving.

Progress, not perfection

Nobody eats perfectly, exercises perfectly or sleeps perfectly. Real life is messier than that. There will be busy weeks, tired evenings, celebrations, setbacks and moments when your usual routines slip.

What matters most is not flawless consistency, but your willingness to return gently to the habits that help you feel well. A single takeaway, a missed workout or a poor night's sleep does not undo your progress. The healthiest mindset is often the softest one: notice what has drifted, make one supportive choice, and begin again without drama.

Perfection is an illusion. Aiming for an 80/20 balance — nourishing choices most of the time, with room for life's treats — is far more sustainable and far more enjoyable.

Conclusion

Good health is rarely the result of one dramatic decision or a sudden burst of intense willpower. It is built through hundreds of small, quiet choices that gradually weave themselves into your everyday life.

You don't need to change everything overnight. Pick one small, comforting habit that feels entirely achievable, and give yourself permission to enjoy the process.

Whenever you need a little clarity along the way, explore Calcaroo's friendly suite of health calculators — including the BMI Calculator, Calorie Needs Calculator, BMR Calculator, Daily Water Intake Calculator, Body Fat Calculator and Ideal Weight Calculator — designed to help you understand your numbers without any judgement.

Take a deep breath, take things at your own pace, and enjoy the journey to feeling your best.

Related Health & Fitness guides

Keep learning with more from the Calcaroo library.