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Vitamin D + Magnesium Calculator

An educational dosing range based on NIH guidance, your sun exposure, and your goals — the same pairing I use myself, from Day 12 of I Wasn't Supposed to Make It, my free 14-Day Life Reset ebook.

D+Mg

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Takes about 20 seconds. Nothing is saved or sent anywhere — this runs entirely in your browser.

"25(OH)D," short for 25-hydroxyvitamin D, is the specific compound your body makes from sun exposure and supplements — it's exactly what a standard blood test measures, not the same number as the IU dose you take. US labs report it in ng/mL; most other countries report the same test in nmol/L (roughly ng/mL × 2.5).

Reference only right now — not yet factored into your range below.

Vitamin D3
—
Source: NIH Office of Dietary Supplements, Vitamin D Fact Sheet.
Vitamin K2
90-120 mcg / day
Taken alongside D3 — K2 helps direct the calcium D3 helps you absorb into bone rather than soft tissue and arteries. Look for a D3 supplement that already includes K2, or add it separately.
Magnesium
Source: NIH Office of Dietary Supplements, Magnesium Fact Sheet. General RDA:
This is educational, not medical advice. These are ranges drawn from NIH and clinical guideline research, not a personal prescription. Anything above general RDA levels, especially Vitamin D above 2,000 IU/day, is worth confirming with an actual blood test and your doctor before starting — more isn't automatically better with fat-soluble vitamins like D, which can build up in the body.

Why D3 and K2 together?

Vitamin D3 increases how much calcium your body absorbs from food. Vitamin K2 is what activates the proteins that direct that calcium into your bones and teeth instead of your arteries and soft tissue, where you don't want it building up. Taking them as a pair is standard practice specifically because of that division of labor — D3 opens the door, K2 tells the calcium where to go.

Every major magnesium type, compared

Not all magnesium behaves the same in your body. Here's the full picture, not just the ones this calculator recommends for your goals above.

Glycinate (Bisglycinate)
Best for: Sleep, relaxation, anxiety
Gentle on the stomach, minimal laxative effect. The most commonly recommended all-purpose form.
Citrate
Best for: Digestion, regularity
Well-absorbed, but the most likely of these to have a loosening effect at higher doses.
Malate
Best for: Muscle pain, fatigue, energy
Paired with malic acid, involved in cellular energy production.
L-Threonate
Best for: Cognitive function, memory, focus
One of the few forms studied specifically for crossing the blood-brain barrier.
Taurate
Best for: Heart health, blood pressure, calm
Paired with taurine, studied for cardiovascular support.
Chloride
Best for: Sensitive stomachs
Often applied topically as a spray or oil, bypassing digestion entirely.
Oxide
Best for: Occasional constipation
Cheapest and most common in multivitamins, but poorly absorbed relative to the others here.
Sulfate (Epsom Salt)
Best for: Bath soaks, sore muscles
Topical only — not used as an oral supplement.
Sources: NIH ODS — Vitamin D Fact Sheet · NIH ODS — Magnesium Fact Sheet

Common questions

How much Vitamin D should I take daily?

The NIH's general adult RDA for Vitamin D is 600-800 IU per day, with a tolerable upper limit of 4,000 IU per day for most adults. People with low sun exposure, darker skin, or a tested deficiency are often studied at higher maintenance ranges (1,000-2,000 IU/day), but any dose above the RDA should ideally be guided by a blood test and a doctor, not guesswork.

Why take Vitamin D3 with K2?

Vitamin D3 increases how much calcium your body absorbs. Vitamin K2 helps direct that calcium into bones rather than soft tissue and arteries. Taking them together is a common practice to support that calcium going where it's actually needed.

How much magnesium should I take?

The NIH RDA for magnesium is about 400-420mg/day for adult men and 310-320mg/day for adult women, including food sources. Supplement form matters — see the comparison above for which type fits your goal.

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