What is a Due Date Calculator?

It is a tool that estimates when a baby is due using Naegele's rule: the first day of the last menstrual period plus 280 days (40 weeks), adjusted for your average cycle length. It also accepts a known conception date or IVF transfer date.

How accurate is the Due Date Calculator's estimated due date?

It is a general estimate from a standard obstetric formula, not medical advice. Only a small fraction of babies arrive exactly on the estimated date; an ultrasound dating scan from a healthcare provider is more precise for an individual pregnancy.

How does the Due Date Calculator handle an IVF transfer date?

Choose IVF transfer, enter the transfer date, and select whether it was a 3-day or 5-day embryo transfer. The calculator back-calculates an equivalent conception date and applies the same 280-day rule.

Why does changing the cycle length change the due date?

Naegele's rule assumes a standard 28-day cycle with ovulation around day 14. A longer or shorter average cycle shifts ovulation, and the calculator adjusts both the conception date and the due date to match.

Does the Due Date Calculator show how many weeks pregnant I am today?

Yes. Alongside the due date it shows today's gestational age in completed weeks and days, plus which of the three trimesters that falls in.

Due Date Calculator Online

Estimate a pregnancy due date from your last period, conception date, or IVF transfer date, right in your browser. A general estimate, not medical advice.

The Due Date Calculator runs entirely in your browser. The dates you enter never leave your device and nothing is uploaded to ArrayKit. This tool gives a general estimate from a standard formula and is not medical advice.

Open the Pregnancy Calculator

About Due Date Calculator

Due Date Calculator estimates when a baby is due using Naegele's rule: the first day of the last menstrual period (LMP) plus 280 days, adjusted for an average cycle length other than 28 days. Enter the LMP directly, or switch to a known conception (ovulation) date, or an IVF embryo transfer date, and the calculator works out an equivalent starting point automatically. Results include the estimated due date, the estimated conception date, and — for today — how many weeks and days pregnant that is and which trimester it falls in. It is a quick way to plan appointments, share a rough timeline with family, or sanity-check a date from a clinic printout. Everything runs locally on your device; the dates you enter are never uploaded. This is a general estimate from a standard formula, not medical advice — an ultrasound dating scan from a healthcare provider is more accurate for any individual pregnancy.

Features

Estimates a due date from the last menstrual period using Naegele's rule
Adjusts the estimate for an average cycle length other than the standard 28 days
Also accepts a known conception/ovulation date or an IVF embryo transfer date
Shows the estimated conception date alongside the due date
Displays today's gestational age in weeks and days, and the current trimester
Shows a progress percentage toward a full 40-week term
Copy a plain-text summary of the due date and pregnancy details in one click
Runs entirely in your browser — the dates you enter never leave your device

How to use the Due Date Calculator

Choose whether you're calculating from your last period, a conception date, or an IVF transfer
Enter the date, and your average cycle length if using the last period or conception date
Read the estimated due date, conception date, and today's gestational age
Copy the summary or switch modes to compare estimates

Example

Input

LMP 2026-01-01

Output

Due date: Oct 8, 2026

Naegele's rule: Jan 1, 2026 plus 280 days lands on Oct 8, 2026.

Common errors & troubleshooting

Due Date Calculator gives a date that doesn't match a clinic's estimate. — Clinics often use an ultrasound measurement rather than the last period alone, which can shift the estimate by several days — the calculator's date is a general LMP-based estimate, not a scan-based one.
Result looks off after switching to a shorter or longer cycle length. — A cycle length above or below 28 days shifts both the ovulation day and the due date; only change it if you actually track your average cycle length, and leave it at 28 if unsure.
IVF transfer date gives a due date that seems too early. — Pick the correct embryo age at transfer (3-day or 5-day) — a 5-day (blastocyst) transfer is closer to conception than a 3-day transfer, so it shifts the estimate a couple of days later.
Cycle length field shows an error. — The average cycle length should be between 20 and 45 days; outside that range the calculator falls back to the standard 28-day assumption.

Frequently asked questions

What is a Due Date Calculator?: It is a tool that estimates when a baby is due using Naegele's rule: the first day of the last menstrual period plus 280 days (40 weeks), adjusted for your average cycle length. It also accepts a known conception date or IVF transfer date.
How accurate is the Due Date Calculator's estimated due date?: It is a general estimate from a standard obstetric formula, not medical advice. Only a small fraction of babies arrive exactly on the estimated date; an ultrasound dating scan from a healthcare provider is more precise for an individual pregnancy.
How does the Due Date Calculator handle an IVF transfer date?: Choose IVF transfer, enter the transfer date, and select whether it was a 3-day or 5-day embryo transfer. The calculator back-calculates an equivalent conception date and applies the same 280-day rule.
Why does changing the cycle length change the due date?: Naegele's rule assumes a standard 28-day cycle with ovulation around day 14. A longer or shorter average cycle shifts ovulation, and the calculator adjusts both the conception date and the due date to match.
Does the Due Date Calculator show how many weeks pregnant I am today?: Yes. Alongside the due date it shows today's gestational age in completed weeks and days, plus which of the three trimesters that falls in.
Is my last period or transfer date uploaded anywhere?: No. The Due Date Calculator runs entirely in your browser. The dates you enter never leave your device and are not uploaded to ArrayKit.

Related tools

Pregnancy Calculator — Track pregnancy progress, trimester and milestones from the due date or LMP.
Conception Calculator — Estimate the likely conception date from a due date or last period.
Ovulation Calculator — Estimate your fertile window and ovulation day from your cycle.
Pregnancy Conception Calculator — Estimate the conception date and fertile window from a known pregnancy.
Period Calculator — Predict your next several periods and fertile windows from your cycle.
Pregnancy Weight Gain Calculator — Estimate a healthy pregnancy weight-gain range from pre-pregnancy BMI.