Pregnancy Week Calculator

What is a pregnancy week calculator?

A pregnancy week calculator tells you how many weeks and days pregnant you are by counting from the first day of your last menstrual period (LMP) to today. Enter your LMP in the tool above and it instantly returns your gestational age in completed weeks plus extra days, which trimester you are in, how far through the pregnancy you are, and your estimated due date.

It answers the question almost everyone asks after a positive test — “how many weeks pregnant am I?” — using the same LMP-based dating that clinics use as a starting point. You can also pick any date instead of today to see how far along you were (or will be) on that day.

How does the pregnancy week calculator work?

The calculator measures gestational age: the time from the first day of your last period to the chosen date. It takes the number of days between the two dates and splits that into whole weeks plus the leftover days.

The exact method the widget uses is:

total days     = today (or chosen date) − LMP
weeks          = floor(total days ÷ 7)
days           = total days − (weeks × 7)
progress       = total days ÷ 280
estimated due date = LMP + 280 days

A few definitions and units:

• LMP — the first day of your last menstrual period, not the day it ended.
• Gestational age — how far along the pregnancy is, reported as completed weeks and days, for example 18 weeks and 2 days.
• Trimester — the first trimester is weeks 1 to 12, the second is weeks 13 to 27, and the third is weeks 28 to 40, all counted from the LMP.
• Progress — total days divided by 280, shown as a percentage of a full 40-week term.
• Estimated due date — the LMP plus 280 days (40 weeks).

Because dating starts at the LMP, the count begins about two weeks before conception. That is why you are counted as roughly 2 weeks pregnant around the time the egg is actually fertilised.

Examples

Each example below matches the tool’s output exactly. They count days from the LMP, so any LMP that lands the chosen date this many days later gives the same result.

Example 1 — 14 days after the LMP

• 14 days = 14 ÷ 7 = 2 weeks and 0 days
• Trimester: first (weeks 1 to 12)
• Progress: 14 ÷ 280 = 5% — this is roughly when conception happens

Example 2 — 70 days after the LMP

• 70 days = 70 ÷ 7 = 10 weeks and 0 days
• Trimester: first (weeks 1 to 12)
• Progress: 70 ÷ 280 = 25% — a quarter of the way through

Example 3 — 98 days after the LMP

• 98 days = 98 ÷ 7 = 14 weeks and 0 days
• Trimester: second (weeks 13 to 27)
• Progress: 98 ÷ 280 = 35%

Example 4 — 200 days after the LMP

• 200 days = 196 + 4, so 28 weeks and 4 days
• Trimester: third (weeks 28 to 40), right at the start
• Progress: 200 ÷ 280 ≈ 71%

At 280 days you reach 40 weeks and 0 days, which is 100% and your estimated due date.

Pregnancy weeks by days since LMP

This table reads straight from the formula above: days since the LMP, the matching weeks and days, the trimester, and progress out of 280 days. Find the row closest to your own day count, or enter your LMP in the tool for an exact result.

Days since LMP	Weeks + days	Trimester	Progress (÷ 280)
14	2w 0d	First	5%
70	10w 0d	First	25%
84	12w 0d	First	30%
91	13w 0d	Second	33%
98	14w 0d	Second	35%
140	20w 0d	Second	50%
196	28w 0d	Third	70%
200	28w 4d	Third	71%
280	40w 0d	Third	100%

What can you use a pregnancy week calculator for?

The same gestational-age estimate supports many points during pregnancy:

• Knowing how far along you are — a quick “how many weeks pregnant am i” answer in weeks and days, any day you check.
• Finding your trimester — seeing whether you are in the first, second, or third trimester for week-by-week expectations.
• Tracking progress — watching the percentage climb toward your due date as a simple countdown.
• Checking a past or future date — picking a different date to see how far along you were at an appointment, or will be for an event.
• Translating to months — using the week number to gauge roughly which month of pregnancy you are in.

For a fixed estimated due date with cycle-length adjustment, pair this with the due date calculator.

Tips and common mistakes

A few points help you read the result correctly:

• Use the first day of your last period, not the last day, and not the day you think you conceived.
• Remember the count starts before conception. Being “8 weeks pregnant” is measured from the LMP, so the embryo is about two weeks younger than the week number.
• Watch the week boundaries. “10 weeks 0 days” means you have completed 10 weeks; the count then runs through 10 weeks 6 days before reaching 11 weeks.
• Know where the trimesters split. Week 13 starts the second trimester and week 28 starts the third, so a few days either side of those marks change the label.
• Don’t over-read the percentage. Progress is measured against a flat 280-day term; full term is a range, not a hard line at 40 weeks.

Limitations and notes

This tool uses a single, widely taught dating method — gestational age from the LMP, with a 280-day term and fixed trimester ranges of weeks 1 to 12, 13 to 27, and 28 to 40. It assumes you know your LMP and that your cycle is fairly regular. For very irregular cycles, an unknown or uncertain LMP, IVF transfers, or recent hormonal birth control, an LMP-based week count is less reliable than a clinical dating ultrasound, which may move your dates. It does not detect twins, ectopic pregnancy, or any complication.

Your inputs stay in your browser. The calculation runs entirely on your device — nothing you type is uploaded or stored, so your dates remain private.

Medical disclaimer: This pregnancy week calculator provides a general estimate for information only and is not medical advice. It is not a substitute for an examination, an ultrasound, or professional judgement. For any care decisions, or if you have concerns about your pregnancy, please consult a doctor, midwife, or qualified healthcare professional.

For more pregnancy tracking, pair this with the ovulation calculator to estimate your fertile window and the date difference calculator for raw day counts between dates, or browse all related tools on the pregnancy & women page.