Iron Intake Calculator
Daily iron mg vs RDA from foods plus supplement.
What it does
Iron hides in small numbers with big jobs. A serving of fortified cereal carries 18 mg while spinach and lentils carry 3 per half cup and beef 2 per 3 oz, against RDAs of 8 mg for men and 18 for women 19-50. One cereal bowl can cover the day; meat alone rarely does.
The tool above sums four lines against the RDA. Enter meat, greens, other foods, and supplement milligrams, pick the group, and it prints total, target, gap, and percent. Defaults total 21 mg against 18: 3 mg over at 116.7 %.
NIH tables supply every constant. Its consumer sheet sets the RDA ladder with vegetarian near-doubling noted, the professional sheet lists cereal 18 with beans 8, liver 5, and lentils-spinach-tofu at 3, and the IOM report stands behind the RDAs with a 45 mg adult upper limit.
Heme and non-heme absorb differently. Meat iron enters readily while plant iron needs vitamin C company, and tea or coffee with meals blocks uptake. Vegetarians multiply needs by 1.8; supplements past food need clinician oversight.
How to use
- Enter meat mg (beef 2/3 oz).
- Enter greens mg (spinach 3).
- Enter other and supplement mg.
- Pick the RDA group.
- Read total first, then the gap.
- Mind the 45 mg adult UL.
Formula
- sources
- Mg from meat, greens, other foods, pills.
- RDA
- 8/11/15/18/27 by age, sex, pregnancy.
RDA and food mg follow NIH ODS consumer and professional sheets with the IOM 2001 report behind them.
Worked example
Example: 21 mg vs 18 RDA
Defaults: other 21 mg, RDA 18.
- Inputs: other foods 21 mg (cereal 18 + spinach 3), RDA 18 (woman 30).
- Total: 21 mg.
- Gap: 21 minus 18 = 3 mg over.
- Share: 21 / 18 x 100 = 116.7 %.
- Tool shows 21 mg, 18 mg RDA, 3 mg over.
Reference table
| Item | mg | Note |
|---|---|---|
| Men 19+ RDA | 8 | Baseline |
| Women 19-50 RDA | 18 | Higher need |
| Pregnancy RDA | 27 | Highest |
| Cereal serving | 18 | 100% DV |
| White beans 1 cup | 8 | Top food |
| Spinach/lentils 1/2 cup | 3 | Each |
Limits
- Planning math only. Absorption varies a lot.
- Heme vs non-heme ignored in totals.
- Vegetarian 1.8x noted, not auto-applied.
- Upper limits need a clinician.
Common mistakes
- Counting one food and ignoring the rest.
- Tea or coffee with iron meals.
- Skipping vitamin C beside plant iron.
- Megadosing past the 45 mg UL.
- Treating the RDA as a ceiling.
Try it yourself
Quick checks. Answers sit tucked under each question.
Meat 2, greens 6, RDA 8?
Total 2 + 6 + 0 + 0 = 8. Gap 8 minus 8 = 0 mg over (100%).
Greens 6, other 18, pregnancy RDA 27?
Total 0 + 6 + 18 + 0 = 24. Gap 27 minus 24 = 3 mg short.
Questions
How is the gap figured?
Sum food and supplement mg against the RDA. Here 21 vs 18 leaves 3 mg over.
What is the iron RDA?
Men 8, women 19-50 18, adults 51+ 8, teens 11/15, pregnancy 27 mg.
How much iron per food?
Cereal 18/serving, white beans 8/cup, liver 5/3 oz, lentils and spinach 3, beef 2.
Can I split food groups?
Yes. Enter meat, greens, other foods, and supplement lines separately.
Do vegetarians need more?
Yes, 1.8x the base RDA (32.4 mg for women 19-50). Note it in limits with a clinician.
Can I overdo iron?
Yes. Adult UL runs 45 mg from all sources; more is not better.
Sources
- NIH ODS: Iron Consumer Sheet (RDA table)
- NIH ODS: Iron Professional Sheet (food mg table)
- IOM/NAS Iron DRI Report (RDA, UL values)