Free tool
Supplement gap calculator
Everyone needs the same RDA. You enter what you ate, we add up the vitamins and minerals, compare them to your personal targets, and show the gap — plus whether food or a supplement is the better way to close it.
Add what you ate to see your gaps.
Everyone needs the same RDA. Add the foods you ate today and we'll add up the vitamins and minerals, compare them to your personal targets, and show which nutrients are short — and whether food or a supplement is the better way to close each gap.
This estimates from a limited food search and standard serving sizes, so treat it as a rough picture, not a diary. For label-accurate tracking across a whole day, log your meals in the CalBurndown app.
Formula & assumptions
The logic here is deliberately simple, and it's the part most supplement marketing gets wrong:
- The requirement is the same for everyone in your age and sex group. Your RDA (Recommended Dietary Allowance) — or an AI (Adequate Intake) where no RDA exists — is set by the National Academies and published by the NIH. It does not go up because you eat a certain way.
- Your intake is what changes. We sum the micronutrients in the foods you add (USDA values, scaled to your serving sizes) and subtract that from your target. Whatever is left is the gap.
- The gap tells you the move. A small gap is usually a food-first fix. A large, persistent gap — or a nutrient your diet can't realistically supply — is where a fortified food or supplement earns its place.
Diet pattern doesn't raise the requirement — it changes the recommendation. A vegan getting almost no B12 from food still has the same 2.4 mcg RDA as everyone else; the difference is that whole plant foods can't supply it, so a fortified source or supplement becomes essential. The only two requirements that genuinely shift on a plant-based diet are iron (set 1.8× higher, since non-heme iron absorbs less well) and zinc (up to ~1.5×, since phytates impair absorption). Iodine, vitamin D, and calcium are flagged as source problems, not bigger numbers.
The B12 absorption nuance. B12 is special: you absorb a smaller fraction of each dose as the dose gets larger. That's why effective supplement doses (often 25–100 mcg/day) dwarf the 2.4 mcg RDA — the RDA assumes efficient absorption of small amounts from food. The target didn't change; the delivery did.
Sodium is a limit, not a floor. Unlike the other nutrients, you aren't trying to “reach” sodium — the goal is to stay under, so we show your running total rather than a gap.
General educational estimate, not medical advice. These are population reference intakes for healthy people, estimated from a limited food search and standard serving sizes. Needs vary with health conditions, medications, malabsorption, and pregnancy. Talk to a doctor or registered dietitian before starting supplements — especially anything approaching a Tolerable Upper Intake Level.
References
USDA FoodData Central. Food composition values (vitamins and minerals per 100 g) used to estimate intake.
National Academies Dietary Reference Intakes (via NIH ODS). Recommended Dietary Allowances and Adequate Intakes — the targets your intake is measured against.
NIH ODS — Vitamin B12 (sources and supplementation). Background on B12 sources and why supplement doses run higher than the RDA.
Per-nutrient fact sheets with the same reference values are available from the NIH ODS Health Professional Fact Sheets.