Calculator

Supplement Timing Optimizer

Check off everything you take. Get back a daily schedule that stops your supplements from blocking each other.

Your day

Fat-soluble vitamins and omega-3s are scheduled here. Absorption of vitamin D roughly doubles when taken with a fat-containing meal versus a low-fat one.

Your stack

Not listed? Anything without a known absorption interaction can go with any meal. The items here are the ones where timing actually changes the outcome.

How this works

Most supplements are sold as if they exist alone. They do not. Taken together in a single morning handful, a common stack will actively reduce its own absorption, and the losses are not small: co-administered calcium can cut non-heme iron absorption by more than half, and zinc and iron compete directly for the same intestinal transporter.

This tool applies four categories of rule to whatever you select, then assigns each item to the time slot that satisfies the most constraints.

1. Divalent mineral competition

Iron, zinc, calcium, copper, and magnesium are all divalent cations, and they share absorption pathways in the small intestine, principally the DMT1 transporter. When two arrive together, the one present in the larger molar quantity wins. Calcium is usually dosed in hundreds of milligrams while iron is dosed in tens, so calcium reliably suppresses iron. The fix is separation, not a lower dose: two hours is enough for most pairs.

Zinc and copper are the pair most worth watching over the long term. Zinc induces metallothionein in intestinal cells, which binds copper and carries it out with the shed cell. Sustained zinc intake above roughly 40 mg/day without matching copper can produce a genuine copper deficiency, with anemia and neurological signs that are frequently misdiagnosed. Separating them helps, but a sane ratio matters more.

2. Food and fat requirements

Vitamins A, D, E, and K, along with CoQ10, curcumin, astaxanthin, lutein, and omega-3 fatty acids, are lipophilic and require dietary fat and bile for micellar absorption. Taking vitamin D with a fat-containing meal rather than on an empty stomach roughly doubles the resulting serum 25-OH-D response. This is the single highest-yield timing change most people can make, and it costs nothing.

The reverse also exists. Iron, levothyroxine, alpha-lipoic acid, and most amino acids absorb best on an empty stomach, because food components bind them or compete for transport.

3. Circadian and functional timing

Some items are timed to physiology rather than absorption. Magnesium glycinate at night takes advantage of its effect on GABAergic tone and sleep onset. Melatonin is a chronobiotic, not a sedative, so the timing relative to your target sleep onset matters more than the dose. Caffeine has a half-life of four to six hours in typical metabolizers, which puts a hard ceiling on how late it can be taken without measurably degrading sleep architecture, even in people who report falling asleep fine.

4. Medication separation

Several common medications create absolute timing windows. Levothyroxine needs four hours of separation from calcium, iron, and magnesium, and is taken on an empty stomach 30 to 60 minutes before food. Probiotics taken alongside an antibiotic are largely wasted, so a two to three hour gap applies. Fiber supplements such as psyllium bind medications non-specifically and should sit at least two hours away from anything else that matters.

Adherence beats optimization. A stack you take consistently at the wrong times outperforms one you abandon because the schedule became a part-time job. If the output below has more than three or four dosing times, collapse the low-stakes items into whichever slot you will actually remember, and preserve only the separations flagged as high priority.

What this tool does not do

It does not check drug-drug interactions, it does not evaluate whether any given supplement is worth taking, and it does not adjust for dose. Interaction magnitude scales with dose: 15 mg of zinc alongside iron is a minor issue, while 50 mg is a real one. Nothing here replaces a pharmacist reviewing your actual medication list.

Talk to a pharmacist or prescriber before changing how you take a prescribed medication. The medication entries in this tool exist to schedule your supplements around them, not to change how or when you take the drug itself. Timing changes to levothyroxine, anticoagulants, and thyroid or seizure medications can have real clinical consequences.

Related calculators

Caffeine Clearance sets your personal caffeine cutoff time.
Vitamin D Repletion sets the dose this schedule places with your fattiest meal.
Creatine Loading covers dosing where timing genuinely does not matter.
Electrolyte Needs for sodium, potassium, and magnesium targets.

References

Lonnerdal B. Dietary factors influencing zinc absorption. J Nutr. 2000;130(5S Suppl):1378S-1383S.

Piskin E, Cianciosi D, Gulec S, et al. Iron absorption: factors, limitations, and improvement methods. ACS Omega. 2022;7(24):20441-20456.

Dawson-Hughes B, Harris SS, Lichtenstein AH, et al. Dietary fat increases vitamin D-3 absorption. J Acad Nutr Diet. 2015;115(2):225-230.

Duncan A, Talwar D, McMillan DC, et al. Quantitative data on the magnitude of the systemic inflammatory response and its effect on micronutrient status. Am J Clin Nutr. 2012;95(1):64-71.

Skelin M, Lucijanic T, Amidzic Klaric D, et al. Factors affecting gastrointestinal absorption of levothyroxine: a review. Clin Ther. 2017;39(2):378-403.

Drakesmith H, Prentice AM. Hepcidin and the iron-infection axis. Science. 2012;338(6108):768-772.