Late period calculator

Check whether your period is late, by how many days, and when a pregnancy test will work.

Free, no account. By the Plum team · Updated September 29, 2026

This page is general information, not medical advice. For questions about your own cycle or health, talk to a doctor, nurse, or other clinician who knows you.

First day of your last period

Average cycle length20 to 45 days

Checking onToday, unless you change it

Pick the first day of your last period. This calculator tells you whether your period is late, and by how many days.

Is my period late?

Your period is due one cycle length after the first day of your last one. Put in that day and how long your cycles usually run, and the calculator above counts how far past the due date you are. Five or more days past it is the usual point where a period counts as late. Anything less is the ordinary swing most cycles have.

The answer is only as good as the cycle length you give it. If you put in 28 but your cycles run 32, it will say you’re four days late on the day your period is actually due. Not sure of yours? Work out your cycle length first.

Is my period late or am I pregnant?

A calendar can’t tell those apart. A pregnancy test can. The NHS says most tests work from the first day of a missed period. If you don’t know when your period was due, test at least 21 days after you last had unprotected sex. A negative test on a very late period is worth repeating a few days later.

How late is my period before I should be worried?

One late period on its own is common and usually settles by the next cycle. The NHS says to see a GP if you’ve missed your period three times in a row, or if you’ve missed one and have other symptoms such as weight gain or loss, tiredness or new hair growth on your face. A pattern that has changed and stayed changed is worth raising too. Our guide to late periods covers the reasons a period runs late and what to bring to the appointment.

Knowing sooner next month

Plum, a period tracker app for iPhone, keeps your start dates, so the due date is already worked out when you wonder. It counts from your own history rather than a number you have to remember.

Common questions

Is this late period calculator free?

Yes. There’s no account and no email box. It runs inside your browser, and the dates you type are never sent anywhere.

How late will my period be if I’m pregnant?

It won’t come. Pregnancy stops periods. Some people get light spotting in early pregnancy, and it can be mistaken for a short, light period. A test is the only way to know.

Can my period be late if I’m not pregnant?

Yes, and often. Stress, illness, travel, a change in weight or training, breastfeeding, PCOS, thyroid problems, perimenopause and hormonal birth control can all push a period back. Our guide to late periods goes through each one.

Is my period late if my cycle is irregular?

It’s hard to say from one average. If your cycles move by a week or more, a single due date will call you late when you aren’t. The irregular period calculator gives you a window instead, and you’re only late once you’re past the end of it.

Does day 1 mean the day my period started or the day it ended?

The day it started. Day 1 is the first day of real bleeding, not spotting. Counting from the day it stopped makes a period look about five days late when it’s on time.

Track it with PlumGet a period tracker that runs this every month.

Plum is an iPhone app. It learns your own cycle length as you log. It reminds you before your period and your fertile window arrive. You can also create a group with your friends. Plum has no ads and never sells your data.

Keep reading

Period calculatorWork out your next six periods, fertile windows and ovulation dates from one date.Period calculator for irregular periodsMeasure the real gaps between your periods. See the range your next one is likely to fall in.How late can a period be?Being a week late once in a while is ordinary. See what counts as late day by day, when a pregnancy test becomes reliable, and when to call a doctor.When do periods come back after stopping birth control?Most periods return within 3 months of stopping the pill, and later after the Depo shot. Here's why a first period runs late, and when to see a GP.