Supplement Cost Calculator: Cost per Day, Month, and Year

Shelf price is the least useful number on a supplement bottle. A $45 tub that lasts three months beats an $18 one that lasts three weeks, and neither label makes that easy to see. This works out what a supplement actually costs you per day, per month and per year, and what you are paying per unit of the thing you are buying it for.

The core formulas

Cost per Serving = Bottle Price ÷ Servings per Bottle

Daily Cost = Cost per Serving × Servings per Day

Monthly Cost = Daily Cost × 30

Annual Cost = Monthly Cost × 12

Value Score = Cost per Serving ÷ Dose per Serving

Watch the serving, not the capsule

The single most common mistake in comparing two bottles. A label saying “120 capsules” and a serving size of 2 gives you 60 servings, not 120. Manufacturers know which of those two numbers looks better on the front of the tub. Enter servings here, not capsules, and if the label only prints capsules then divide first.

Value score, and why bottle price lies

Two magnesium bottles at $20 are not the same purchase if one is 200 mg a serving and the other is 400 mg. The value score divides cost per serving by the dose in that serving, so it answers “what am I paying per milligram” rather than “what am I paying per pill”. Lower is better. It is the only comparison that survives contact with a supplement aisle, and it is why the enormous-looking tub is sometimes the cheap one.

Do not push it further than it goes. Cost per milligram says nothing about whether a form is absorbed well. Magnesium oxide is cheap per milligram and poorly absorbed. Magnesium glycinate costs more per milligram and mostly gets in. Use the score to compare like against like.

Worked example

Magnesium glycinate, $32 for a bottle of 120 capsules, serving size 2 capsules, 400 mg per serving.

That is 60 servings, so $0.53 per serving and $0.53 a day at one serving daily. Monthly $16.00, annual $192.00. One bottle lasts 60 days, so you need 7 bottles a year. Value score: $0.53 for 400 mg works out at $1.33 per 1,000 mg.

Typical monthly supplement costs

Rough retail ranges, and they move with region and year:

Buying a 90 or 180 day supply usually cuts cost per serving by 25 to 40% against a 30 day bottle. That only pays off if you finish it. Fish oil in particular goes rancid, and a rancid capsule is worse than no capsule, so check the expiry date before you scale up on anything you take irregularly.