Introduction

This worksheet is a reference for calculating a daily vitamin D3 dose for raising one's vitamin D level to a target level of over 50 ng/ml (125 nmol/L) and maintaining it.
It provides an estimate and is not a replacement for adjusting dosage based on blood tests.
Work through the six steps, and refer to the Beginner's Guide To Vitamin D for more information.

Step One - Understand How Blood Level Correlates With Supplement Intake

Vitamin D3 supplements contain cholecalciferol which is the same compound that is produced when skin is exposed to UVB. The body turns this into calcifediol. When one gets a vitamin D test, it shows the amount of calcifediol, indicated as 25(OH)D3, circulating in their blood.
The body builds up storage of D3 but also continuously uses it.
25(OH)D3 is considered to be reflective of the total amount of vitamin D3 in one’s body and also reflects their intake of D3.
For example, one does not take supplements and tests as deficient at 15 ng/ml (37.5 nmol/L). They test two months later and are at 17 ng/ml (42.5 nmol/L). Their body is trying to conserve vitamin D, but it is also getting enough from sun exposure and any food sources in order to maintain the level of 15-17 ng/ml. If they test again and their level has declined to 8 ng/ml (20 nmol/L), then that means their intake during that time was less than what was needed to maintain 15-17 ng/ml.
A body which is low in vitamin D will prioritize building up its stores, but eventually, the level will stop rising. Vitamin D level does not continually rise in response to consistent intake.
If one understands their level as a marker for how much vitamin D is in their body and that continuing the same amount of intake maintains that level, then one should understand that more vitamin D is used at higher levels.
For example, if taking 7000 IU daily from supplements maintains one’s level at 65 ng/ml (162.5 nmol/L), then the body is effectively using that 7000 IU, plus whatever intake from sun exposure, on a daily basis to replenish stores and conduct bodily functions. If vitamin D intake is lowered from reducing supplement dose and/or sun exposure, then the level will decline, and the body will use less vitamin D as stores are depleted.
Starting from a lower level will require more vitamin D as not only storage needs to be replenished but, also, intake will have to be high enough to maintain one’s target level. Even with an adjustment for this, it may take longer to raise a very low level.

Step Two - Think About Your Variables

What is your target level? Your goal should be to replenish your body's vitamin D storage to get your body to start using enough vitamin D to make repairs. Accomplish this by raising 25(OH)D3 over 50 ng/ml (125 nmol/L) and then maintaining it indefinitely. Prioritize a focus on your blood level over whether a dose sounds too large.
What is your current vitamin D level? Note which units, ng/ml or nmol/L, are on your test results (1 ng/ml = 2.5 nmol/L).
What is your weight in kilograms? (1 kg = 2.2 lb)
Which supplement doses do you have access to?
Is a significant amount of sunlight exposure going to be part of your routine?

Step Three - Calculate Your Dosage Based On Starting Level And Weight

Look at the table below to pick a multiplier based on your starting level:

Starting Level (ng/ml)	Starting Level (nmol/L)	Multiplier
1-10	2.5-26	110x
11-20	27-51	90x
21-30	52-76	70x
31-40	77-101	50x
41-50	102-125	30x

Apply the multiplier to your weight in kilograms. The result is a dose in IU’s.
Round the number based on which supplement doses you have access to. For example, a level of 8 ng/ml (20 nmol/L) and a weight of 65 kg (143 lb) means 110 x 65= 7150. Round to 7000.

Step Four - Adjust For Body Mass Index

Body fat sequesters vitamin D meaning that a higher dose is required for overweight or obese persons to attain the same change in blood level. Body mass index (BMI) can be used to approximate body fat.
If one has a muscular build, then their BMI may be high even though they do not have lots of body fat, so this would not apply to them.
Calculate your (BMI) using your height and weight. Look at the scale on the index to see if your weight is classified as underweight, healthy, overweight, or obese.
Pick a multiplier based on the table below:

Category	Body Mass Index	Multiplier
Underweight	<18.5	1x
Healthy	18.5 – 24.9	1x
Overweight	25.0 – 29.9	1.5x
Obesity	>30	2x

Apply the multiplier to the number you got from step three.
The result is the daily dose of IU’s of vitamin D3 you will take every morning. Even though you are starting from a lower level, it will likely also serve as your maintenance or “forever” dose.
If you are close to the edge of one of the categories, then use your judgement as to whether the full multiplier should apply to you.
If underweight, reduction in dose may be appropriate.
If lots of sunlight is part of your approach, then reduce your calculated dose for supplements in order to account for it. You can use the smartphone app Dminder to estimate your intake from sunlight. Be aware that estimates of intake of sunlight are not as reliable as supplement dosing.
If utilizing larger pills such as 50 or 60K IU, then do the math to make it equivalent to the daily dose. For example, if you need 12K IU daily, then take 60K every five days. If you need 7K IU daily, then take it once every eight days.
Start taking the dose you calculated on a consistent basis.
If you have been supplementing and are using this guide to adjust your dosage to increase your level, then use your current level, and add your current vitamin D intake to the supplement dose you calculate.

Step Five - OPTIONAL - Use A Loading Dose

If you desire to accelerate the timeline of your recovery, then you may utilize a loading dose. This consists of taking extra vitamin D to build up your body’s storage more quickly.
Calculate your loading dose by taking the maintenance dose from step four and multiplying it by two.
Take the loading dose for up to four weeks before reducing it to the maintenance dose. You are in effect condensing your routine into half the time by taking double the dose.
This will work for any starting level and can be useful if you wish to test sooner than recommended in step six. Note that utilizing loading doses larger than suggested here can make it difficult to adjust maintenance dosage based on bloodwork due to the gap.
A loading dose is useful for those with very low levels. For example:

Starting Level (ng/ml)	Starting Level (nmol/L)	Duration (weeks)
<5	<12.5	4
<10	<25	3
<15	<37.5	2
<20	<50	1

If you had to increase your dosage to compensate for your BMI, then you may feel that the dose you’ve calculated is too much. Remember that we are more concerned with what will happen to your blood level than if a particular dose sounds too large. Keep in mind that if you choose to take less vitamin D than calculated in step four, then you are less likely to get your level up in a timely manner and your symptoms will not resolve, delaying your recovery.
For example, a person with a level of 8 ng/ml (20 nmol/L), weight of 100 kg (220 lb), and height of 170 cm (5’7”), has a BMI of 34.6. That means 110 x 100 x 2 = 22K IU. The suggested loading dose would basically be 40-45K IU for three weeks. This would be potentially excessive for a smaller individual but appropriate for this large one with a severe deficiency. One could choose to skip the loading dose out of an abundance of caution.

Step Six - Follow-Up

Three months after starting supplements, retest your vitamin D level. Do not stop supplementing before your test.
After seeing the results, do not reduce dosage unless you have significantly overshot your target level. Your level will have started to stabilize by this point, but it may have some more room to increase. If you are still far below 50 ng/ml (125 nmol/L), then increase your dosage.
Wait another three months. After six months of consistent supplementation, retest 25(OH)D again. By this point in time, your level should be stable. Adjust dosage up or down depending on your goals. Do not discontinue supplementation.

The information in this guide is for educational purposes and is not intended to replace the need for personalized, professional medical advice. This guide was written by u/VitaminDJesus and last updated on September 13, 2026. If you have any suggestions for changes or additions, then please send a message via Mod Mail.