What are DHA and EPA, and how do they differ?

DHA and EPA are two different omega-3 fatty acids. They differ in their molecular structure and can appear in different amounts in a supplement. “Omega-3”, “fish oil” and “DHA+EPA” therefore mean different things.^[1][2]

When reading a label, separate three details: how much oil the product contains, how much DHA and EPA it declares, and how much product those figures refer to. Two packs with the same number on the front can have different compositions.

What do DHA and EPA stand for?

DHA stands for docosahexaenoic acid. EPA stands for eicosapentaenoic acid. Both are polyunsaturated fatty acids in the omega-3 family.^[1]

Their differences include the length of their carbon chain and the number of double bonds:

Sources for the structural details: NIH Office of Dietary Supplements and ChEBI.^[1][4] The numbers in the notation describe the molecule. They are neither milligram amounts nor intake instructions.

Is all omega-3 DHA or EPA?

No. Omega-3 is a family of fatty acids. It also includes ALA, short for alpha-linolenic acid. Flaxseed oil is one source of ALA.^[1][2]

An amount of ALA declared on a label does not count as DHA or EPA in that product. “Total omega-3” can also differ from DHA+EPA because it may include other omega-3 fatty acids.

A label saying only “1,000 mg omega-3” therefore does not establish how much DHA or EPA the product contains. You need a breakdown or an explicitly declared DHA+EPA total.

Are DHA and EPA only found in fish oil?

No. Supplements containing DHA and EPA can use fish oil, krill oil or algal oil, for example. Algal oil products vary: some mainly declare DHA, while others also declare EPA.^[1]

The oil source is not a fixed recipe. Omega-3 products can contain predominantly DHA, predominantly EPA or other proportions.^[3] Check the label for the specific pack to establish its declared amounts.

“Algal oil” alone does not identify every other ingredient either. Check the full ingredients list to find out what the capsule shell or other components are made from. Read more about the sources in Fish oil or algal oil: what is the difference?.

What does DHA+EPA mean on a label?

DHA+EPA is the sum of the two declared amounts, expressed on the same basis. If DHA is listed per capsule and EPA per two capsules, first convert them to the same unit.

This fictional example refers to one capsule for both products. The figures are invented to explain the difference; they are not test results.

Both labels add up to 500 mg DHA+EPA per capsule. Yet product A has more DHA and product B has more EPA. The same total does not make the compositions identical.

The ratios differ too. In DHA:EPA order, A has a ratio of 3:2 and B has a ratio of 3:7. That describes the proportions; it is neither a quality judgement nor advice about which ratio you need.

Why is the amount of oil different?

Oil is the mixture that contains the fatty acids. The milligram amount of oil is therefore a different figure from its DHA+EPA content.

Suppose product A’s fictional label also declares 1,000 mg fish oil per capsule. According to that label, this includes 300 mg DHA and 200 mg EPA: 500 mg combined. Do not add the 1,000 mg fish oil to that 500 mg. The DHA and EPA are part of the oil.

A percentage also needs a clear basis. A percentage of the oil and a percentage of all fatty acids are not automatically equivalent. Without knowing the basis, you cannot simply convert the percentage into milligrams per capsule.

For the full reading sequence, including liquid oils and gummies, see How to read an omega-3 supplement label.

What if only DHA is listed?

You know how much DHA the label declares. That does not establish how much EPA is present. An absent EPA declaration does not mean a declaration of 0 mg EPA.

Distinguish these situations:

• DHA and EPA listed separately: add the amounts after putting them on the same basis.
• Only a combined DHA+EPA total listed: the total is known, while the split may remain unknown.
• Only DHA listed, without a DHA+EPA total: the DHA amount is known; an exact DHA+EPA total has not been established from this information.

Do not fill a gap using the composition of a similar product. A missing declaration does not, by itself, establish anything about the supplement’s quality.

What can these figures help you compare?

You can compare the declared amounts of DHA, EPA and their combined total. To compare prices, divide the pack price by the grams of DHA+EPA in that pack, provided the available information establishes that total.

This price per gram gives costs a common basis, but does not show the relative proportions. Check the individual amounts too. The price calculation does not establish a verdict on composition or which supplement suits a person.

On SUPPFAX, DHA+EPA amounts declared on the label form the basis of the price calculation. A label declaration remains a manufacturer’s statement. A measurement requires a separate laboratory report, with its source, date and the material examined.

Sources

Consulted on 31 October 2026.

1. NIH Office of Dietary Supplements — Omega-3 Fatty Acids, Health Professional Fact Sheet. For molecular differences, ALA and variation between supplements. Stated source update: 22 August 2025. ↩ ↩ ↩ ↩ ↩
2. Voedingscentrum — Omega 3 en omega 6 (Dutch). For Dutch terminology and the classification of omega-3 fatty acids. ↩ ↩
3. GOED Voluntary Monograph, version 8.1, 6 January 2022 (PDF). For differing DHA and EPA proportions and expressing their amounts individually and as a combined total. ↩

4. EMBL-EBI ChEBI — DHA, CHEBI:28125 and EPA, CHEBI:28364. Primary database records for molecular structure. ↩