1 in 5

women of reproductive age have iron deficiency anaemia

35ml

average blood lost per cycle — but ranges from 10ml to 200ml+

18mg

daily iron RDA for women 19–50, more than double the male RDA

About your period

All answers are approximate — give your best estimate. Nothing is stored or shared.

Life stage

How many days does your period last?

5 days

How would you describe your overall flow?

Additional details

Clots larger than a 50p / quarter coin? Large clots indicate higher blood loss

Spotting days before or after? Extra light bleeding outside main flow days

Pain or flooding limiting daily activity? Can indicate heavier actual blood loss than perceived

Diet type (affects iron absorption)

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Your monthly iron cost

Fill in your period details on the left — you'll see your estimated iron loss, how it compares to average, and what you need to eat to replace it.

Estimated iron lost per cycle

—

~— ml blood

+— mg/day above baseline

Your blood loss vs. average (35 ml)

0 ml Your loss: — ml 100+ ml

Low

<15 mg

Moderate

15–30 mg

High

31–50 mg

Very High

50+ mg

—%

of your daily iron RDA used just by your period

— mg

extra iron needed per day to offset your period loss

Your period's iron demand vs. daily RDA

0 RDA: 18 mg/day

—

To replace this with diet alone, you need per week:

—

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Check your iron deficiency risk → Heavy periods are the #1 cause of iron deficiency in women. Take our screener to assess your symptoms.

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Track your cycle & symptoms → Monitor your flow over time to spot patterns and discuss with your doctor.

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Why periods and iron deficiency are so closely linked

Blood is rich in haemoglobin, and haemoglobin is 70% iron. Every millilitre of blood lost takes approximately 0.5 mg of iron with it. For a woman with a typical 35ml period, that's around 17–18 mg of iron per cycle — close to an entire day's recommended intake, lost in just 5 days.

Women with heavy menstrual bleeding (defined clinically as more than 80ml per cycle) may lose 40–100mg of iron or more each month. Without significant dietary compensation or supplementation, this creates a chronic monthly deficit that progressively depletes iron stores — often silently, for years, before symptoms become obvious.

80mlClinical threshold for heavy menstrual bleeding (HMB)

0.5mgIron lost per ml of menstrual blood

10–20%Dietary iron actually absorbed (non-heme vs. heme matters)

2–5 yrsHow long iron deficiency can develop silently before diagnosis

Medical note: This calculator estimates iron loss based on self-reported flow and is for informational purposes only. It cannot diagnose iron deficiency or heavy menstrual bleeding. If you suspect heavy or abnormal periods, or have symptoms of iron deficiency (fatigue, pallor, breathlessness, hair loss), please speak to a GP. A simple blood test (ferritin + CBC) is the accurate way to assess your iron status.