🧮 Free tool

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.

Takes about 20 seconds Nothing saved or sent anywhere
⚡ The short version

Three quick stations, light, load, and goal, then one generated range.

D3, K2, and Magnesium together, sourced from NIH guidance, not a generic multivitamin dose.

Nothing is saved or sent anywhere. The whole calculation runs in your browser.

Pick cognitive function as a goal and the exact magnesium form I personally use appears.

Calibrate your baseline

Get your range

All three stations stay visible the whole time, nothing is hidden behind a wizard. Answer in any order, then generate your range at the bottom.

01

Light

"25(OH)D," short for 25 hydroxyvitamin D, is the specific compound your body makes from sun exposure and supplements, 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 times 2.5).

More melanin blocks more UVB, so the same number of minutes in the sun produces less Vitamin D in deeper skin tones. This only adjusts the estimate when you haven't been tested, since an actual blood test already accounts for it.

02

Load

Heavy sweating and training increase magnesium losses, so the NIH notes very active people may need more than the general RDA.

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

03

Goal

Pick at least one goal above so I know which magnesium type to recommend.

The result

Your range

Vitamin D3
—
Source: NIH Office of Dietary Supplements, Vitamin D Fact Sheet.
Vitamin K2
90 to 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:
Why this range

Your D3 range comes from your sun exposure and test answers above (see the note under Vitamin D3), your magnesium RDA comes from your biological sex and activity level, and your magnesium type recommendation comes directly from the goals you picked. Body weight is not currently factored in, that field is reference only for now.

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.

The reference library

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 is the full picture, not just the ones this calculator recommends for your goals above.

Glycinate (Bisglycinate)
Best for: Sleep, relaxation, anxiety
200 to 400mg elemental, 30 to 60 minutes before bed. Gentle on the stomach, minimal laxative effect. The most commonly recommended all purpose form.
Citrate
Best for: Digestion, regularity
200 to 400mg elemental, split into two doses to ease in. Well absorbed, but the most likely of these to have a loosening effect at higher doses.
Malate
Best for: Muscle pain, fatigue, energy
300 to 400mg elemental, morning or with meals. Paired with malic acid, involved in cellular energy production.
L-Threonate
Best for: Cognitive function, memory, focus
~140 to 160mg elemental (from 1,000 to 2,000mg of the compound), evening. One of the few forms studied for crossing the blood brain barrier.
Taurate
Best for: Heart health, blood pressure, calm
250 to 500mg elemental, split morning and evening. Paired with taurine, studied for cardiovascular support.
Chloride
Best for: Sensitive stomachs
~100 to 150mg elemental (roughly 4 to 6 sprays), applied to skin after a shower, bypassing digestion. Absorption varies person to person.
Oxide
Best for: Occasional constipation
250 to 400mg elemental, with food. Cheapest and most common in multivitamins, but poorly absorbed relative to the others here.
Sulfate (Epsom Salt)
Best for: Bath soaks, sore muscles
1 to 2 cups in a warm bath, soak 15 to 20 minutes. Not an oral dose, skin absorption evidence here is genuinely weak, more established as a relaxing soak than a proven magnesium delivery method.
On combining these: the NIH sets a tolerable upper limit of 350mg/day of elemental magnesium specifically from supplements (separate from total intake including food, which has no set upper limit since dietary magnesium isn't linked to toxicity). If you're combining more than one type above, add up the elemental totals rather than each dose in isolation.

Sources: NIH ODS, Vitamin D Fact Sheet · NIH ODS, Magnesium Fact Sheet

Common questions

Frequently asked questions

How much Vitamin D should I take daily?

The NIH's general adult RDA for Vitamin D is 600 to 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 to 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 to 420mg/day for adult men and 310 to 320mg/day for adult women, including food sources. Supplement form matters, see the comparison above for which type fits your goal.

I Wasn't Supposed to Make It, A 14 Day Roadmap Back to Health, by Sama Alabed

🎁 Free ebook

This is one piece of the full 14 Day Life Reset

Everything it took me years to learn the hard way, the protocol I wish someone had handed me on day one. Free, no strings. Drop your email and I'll send it your way.

No spam, ever. Unsubscribe anytime.

Built by samā·says, reviews and protocols based on real, cited research.