Menstrual Iron Loss Calculator
Estimate iron lost through menstruation based on flow volume and cycle length, and see how that translates into daily dietary iron requirements.
🩸 Women's Health📐 Iron lost ≈ blood volume × 0.5 mg per mL; spread across the cycle🏥 Health
Flow level
Cycle length (days)
Period duration
Diet type
Please enter valid values.
Formula & Reference
| Variable | Symbol | Formula | Units |
|---|---|---|---|
| Menstrual Iron Loss Calculator | — | Iron lost ≈ blood volume × 0.5 mg per mL; spread across the cycle | mg per day |
Step-by-Step Examples
Example 1
Normal Flow
Normal flow, 28-day cycle, mixed diet.
- Estimated volume: 50 mL per period
- Iron lost = 50 × 0.5 = 25 mg per cycle
- Spread over 28 days = 0.89 mg/day
- RDA remains 18 mg/day given limited absorption
✓ 0.89 mg/day lost — RDA 18 mg/day
Example 2
Heavy Flow
Heavy flow, 26-day cycle, mixed diet.
- Estimated volume: 100 mL
- Iron lost = 50 mg per cycle
- Spread over 26 days = 1.92 mg/day
- More than double the normal-flow loss
✓ 1.92 mg/day — worth clinical review
Example 3
Vegetarian, Normal Flow
Normal flow, 30-day cycle, vegetarian.
- Iron lost = 25 mg per cycle = 0.83 mg/day
- Non-haem iron absorbs poorly, so the target rises
- Adjusted target = 18 × 1.8 = 32 mg/day
✓ Target approximately 32 mg/day
Real-World Applications
Deficiency Risk
Heavy menstrual bleeding is one of the most common causes of iron deficiency anaemia in premenopausal women worldwide.
Dietary Planning
Understanding the scale of monthly loss makes the relatively high iron RDA for menstruating women considerably more intuitive.
Athletic Performance
Low iron stores impair endurance performance well before anaemia develops, which makes menstruating athletes a monitored group.
Clinical Discussion
Quantifying flow gives a concrete starting point for a conversation about heavy menstrual bleeding.
Common Mistakes to Avoid
⚠️
Assuming heavy periods are simply normal
Flow above roughly 80 mL per cycle meets the definition of heavy menstrual bleeding, which is treatable and frequently causes iron deficiency.
⚠️
Self-treating with iron without testing
Iron deficiency should be confirmed with ferritin before supplementing, and persistent deficiency needs its cause identified rather than just corrected.
⚠️
Estimating flow volume precisely
Self-reported flow is imprecise. Product counts and the pictorial blood loss assessment chart give rough guidance, but exact volumes are hard to determine outside research settings.
Frequently Asked Questions
How much iron is lost during a period? ▾
Roughly 0.5 mg of iron per millilitre of blood, so a typical 50 mL period loses about 25 mg of iron across the cycle.
Why is the iron RDA so much higher for menstruating women? ▾
Because only about 10 to 15% of dietary iron is absorbed, so intake must substantially exceed losses to maintain stores — hence 18 mg per day versus 8 mg for men.
What counts as heavy menstrual bleeding? ▾
Clinically, blood loss above 80 mL per cycle, or bleeding that interferes with physical, emotional, or social quality of life.
Should I take iron supplements if I have heavy periods? ▾
Get ferritin tested first. Heavy bleeding is a common cause of deficiency, but supplementation should follow confirmation and the bleeding itself may be treatable.
Does the contraceptive pill affect iron loss? ▾
Hormonal contraception often reduces menstrual blood loss, and some methods stop periods entirely, which can meaningfully improve iron status.