Can you tell PMS from early pregnancy by your symptoms?

Usually not, and almost never before your period is due. The NHS's own list of early pregnancy signs describes breasts that "may become larger and feel tender, just as they might do before your period". Tiredness, mood changes and food cravings appear on both its PMS list and its pregnancy list, and cramps are common in both. What separates the two is mostly timing, plus a handful of symptoms that turn up on only one side.

For why symptom-spotting after ovulation is so inconclusive, see two week wait symptoms; for the pregnancy list alone, early pregnancy symptoms before a missed period.

PMS vs pregnancy symptoms, side by side

The table uses the NHS symptom lists for PMS and early pregnancy, with the PMS timing rule from the American College of Obstetricians and Gynecologists (ACOG). "Not listed" means not on that list, not that it never happens.

Symptom	PMS	Early pregnancy	Tells them apart?
Timing	In the 5 days before a period, ending within 4 days of it starting (ACOG)	Usually from around 4 to 6 weeks pregnant (NHS)	Yes, once your period is due
Breast changes	Breast tenderness	Larger and tender, "just as they might do before your period"	No
Cramps	Bloating or cramping	Stomach pains or cramps are common in pregnancy	No
Spotting	Not listed	A bleed like a very light period, around when your period is due	Partly
Nausea	Not on the NHS list; ACOG includes gastrointestinal symptoms	Feeling or being sick, any time of day or night	Leans pregnancy
Discharge	Not listed	More discharge, without soreness or irritation	Weak
Mood	Mood swings; irritable, anxious or emotional	Changes in mood	No
Tiredness	Tiredness or trouble sleeping	Extremely tired after your usual activities	No
Appetite	Changes in appetite or food cravings	Cravings, or losing interest in foods you enjoy	No
Peeing more	Not listed	More often, without pain or discomfort	Leans pregnancy
Taste and smell	Not listed	Metallic taste; sensitivity to smells	Leans pregnancy
Headaches, spots, greasy hair	Listed	Not on the early-signs list	No

Which symptoms actually point towards pregnancy?

Your period not arriving. The NHS puts a missed period first on its list of early signs. ACOG's definition of PMS requires symptoms that end within 4 days after a period starts, so symptoms that carry on past the day your period was due, with no period, are no longer behaving like PMS.
Symptoms only on the pregnancy list. A metallic taste, sensitivity to smells, peeing more often without pain, and feeling sick are NHS pregnancy signs that are not on its PMS list. But the NHS says early signs usually start at around 4 to 6 weeks of pregnancy, counted from the first day of your last period. On a regular 28-day cycle, 4 weeks is the day your next period would have started, so these signs rarely help before then.
A bleed that stays light. The NHS describes implantation bleeding as "a bleed similar to a very light period, with some spotting or only a little blood". Implantation bleeding vs a period compares the two.

For breasts specifically, see sore breasts in early pregnancy.

Why symptoms cannot settle it before your period is due

Pregnancy tests detect human chorionic gonadotrophin (hCG), which the NHS says "starts to be produced around 6 days after fertilisation". Before the embryo implants, a pregnancy cannot be detected at all.

Implantation can come later than people assume. Allen Wilcox and colleagues at the US National Institute of Environmental Health Sciences tested serial first-morning urine samples with an extremely sensitive hCG assay and reported in JAMA in 2001 that 14 of 136 pregnancies, 10%, had not implanted by the first day of the missed period. On their figures, the best any hCG-based test could do on that day was to detect 90% of pregnancies, rising to 97% a week later.

When does a pregnancy test become reliable?

From the first day of your missed period. The NHS says most tests can be used from then, and some very sensitive tests earlier. If you do not know when your period is due, test at least 21 days after you last had unprotected sex. You can use urine from any time of day.

A positive result is almost certainly correct; a negative is less reliable, particularly if you tested too early. If you still think you are pregnant, wait a few days and test again, and speak to your GP if a second test is negative and your period has not arrived. The pregnancy test timing calculator dates your earliest sensible test. Already have a result? See pregnancy symptoms but a negative test or a faint line on a pregnancy test.

If it turns out to be PMS

ACOG's criteria for PMS are symptoms in the 5 days before a period for at least three cycles in a row, ending within 4 days of it starting, and interfering with some normal activities. The NHS suggests a symptom diary for at least 2 cycles to take to your GP. ACOG notes that depression, anxiety and perimenopause can all mimic PMS; if you are in your 40s, see pregnancy or perimenopause.

When to get help

Possible ectopic pregnancy. The NHS says to contact your GP or call NHS 111 if you think you might be pregnant and have a combination of symptoms such as bleeding that starts and stops or is watery and dark brown, tummy pain low down on one side, shoulder tip pain, or discomfort when you poo or pee, "even if you haven't had a positive pregnancy test". These usually develop between the 4th and 12th weeks.
Emergency. Call your local emergency number (999 in the UK and Ireland, 911 in the US and Canada, 000 in Australia, or 111 in New Zealand) for a combination of sharp, sudden and intense tummy pain, feeling very dizzy or fainting, and feeling sick, which the NHS lists as signs of a ruptured ectopic pregnancy.
Severe premenstrual symptoms. The NHS says to call 999 or go to A&E if you have symptoms of premenstrual dysphoric disorder (PMDD) and feel suicidal, and to see a GP if PMS is affecting your daily life.

Frequently asked questions

Can you have PMS symptoms and still be pregnant?

Yes. Sore breasts, tiredness, mood changes and food cravings appear on both the NHS list of PMS symptoms and its list of early pregnancy signs, so feeling premenstrual does not rule pregnancy out. If your period does not arrive, take a test: the NHS says most tests work from the first day of a missed period.

Do pregnancy cramps feel different from period cramps?

Not in a way you can rely on. The NHS lists cramping among common PMS symptoms and says stomach pains or cramps are common in pregnancy too. Mild pain that eases when you rest, change position, poo or pass wind is probably nothing to worry about. Cramps with bleeding, or pain low on one side, need advice.

Is nausea a sign of PMS or pregnancy?

Feeling or being sick is an NHS early pregnancy sign but not on its list of common PMS symptoms, although ACOG includes gastrointestinal symptoms in PMS. It leans towards pregnancy, but early signs usually start at around 4 to 6 weeks, so nausea a week before your period is due is a weak clue.

Is discharge different before a period and in early pregnancy?

The NHS lists more vaginal discharge, without soreness or irritation, as an early pregnancy sign; discharge is not on its PMS list. On its own it is a weak clue. Discharge with soreness or irritation is not the sign the NHS means, and is worth getting checked.

Is there a quiz that can tell if I'm pregnant or about to start my period?

No. A quiz can only add up the symptoms you report, and the main ones are on both NHS lists. Even a test is limited early: in one study, 10% of pregnancies had not implanted by the first day of the missed period. Test from that day, and again a few days later if negative.

PMS or Pregnancy? The Symptoms Side by Side