Vitamin D Dose Calculator

Calculator Inputs

Age in years

Weight in kg

Indication Deficiency correction Maintenance support Prevention only

Baseline 25(OH)D

Baseline unit ng/mL nmol/L

Target 25(OH)D

Target unit ng/mL nmol/L

Current supplement intake

IU/day

Supplement strength 400 IU per unit 800 IU per unit 1,000 IU per unit 2,000 IU per unit 5,000 IU per unit 50,000 IU per unit

Schedule preference Show daily plan first Show weekly plan first

Supplement form Vitamin D3 Vitamin D2

Pregnant No Yes

Lactating No Yes

Obesity No Yes

Malabsorption history No Yes

Interacting medicines No Yes

Hypercalcemia, stones, CKD, granulomatous disease No Yes

Calculate Vitamin D Dose Reset

Example Data Table

These examples are educational illustrations. Real dosing depends on labs, diagnosis, calcium status, medications, and clinician judgment.

Formula Used

• Unit conversion: ng/mL = nmol/L ÷ 2.5, and nmol/L = ng/mL × 2.5.
• Weekly equivalent: weekly IU = daily IU × 7.
• Extra supplement estimate: additional IU/day = recommended IU/day − current supplement IU/day, floored at zero.
• Units needed: units/day = additional IU/day ÷ strength per capsule, tablet, or dropper.
• Course total: total IU = daily IU × 7 × planned weeks.
• Dosing engine: the calculator combines age band, baseline 25(OH)D range, pregnancy status, high-risk flags, and maintenance rules to estimate a plan.

How to Use This Calculator

1. Enter age, weight, and the reason for supplementation.
2. Enter the latest 25(OH)D result and choose the correct unit.
3. Enter the target level your clinician wants or keep a common goal such as 30 ng/mL.
4. Add current supplement intake so the tool estimates only the additional amount.
5. Choose the supplement strength to see how many units are needed daily or weekly.
6. Turn on obesity, malabsorption, or interacting medicines if those risks apply.
7. Use the caution option for kidney disease, kidney stones, hypercalcemia, or granulomatous disease.
8. Press calculate and review the result, warnings, maintenance range, and recheck timing.

Frequently Asked Questions

1. What vitamin D blood value should I enter?

Enter your serum 25-hydroxyvitamin D result, often written as 25(OH)D. Do not enter 1,25-dihydroxyvitamin D unless a specialist explicitly asks for that.

2. Can this calculator replace a prescription plan?

No. It provides an educational estimate. Prescription regimens depend on diagnosis, calcium level, kidney function, symptoms, and follow-up plans.

3. Why does obesity or malabsorption change the estimate?

Both can reduce the rise in blood vitamin D after supplementation. These users often need higher supervised doses and closer repeat testing.

4. Why does the result show both daily and weekly dosing?

Some repletion plans are taken daily, while others use weekly totals. Showing both helps convert one schedule into another when clinically appropriate.

5. Is vitamin D2 or D3 better?

Both can treat deficiency, but vitamin D3 often raises 25(OH)D more reliably. Many clinicians prefer D3 for routine outpatient supplementation.

6. Why does the tool warn about higher blood levels?

Very high vitamin D intake can cause toxicity and hypercalcemia. When the baseline is already high, increasing supplements may be unsafe.

7. Should I take vitamin D with food?

Many people absorb vitamin D better when they take it with a meal containing some fat. This can be useful during short repletion courses.

8. When should vitamin D levels be rechecked?

Common follow-up windows are six to twelve weeks after a dose change, but exact timing depends on deficiency severity and clinical risk.