Beta-Oxidation Calculator
Calculate total ATP from beta-oxidation of saturated and unsaturated fatty acids.
Counting the Rounds
Each round of beta-oxidation removes two carbons as acetyl-CoA and produces one NADH and one FADH2. The arithmetic follows from a single fact: the final round yields two acetyl-CoA rather than one, because a four-carbon fragment splits into two.
| Fatty acid | Carbons | Rounds | Acetyl-CoA | NADH | FADH2 |
|---|---|---|---|---|---|
| Caprylate | 8 | 3 | 4 | 3 | 3 |
| Palmitate | 16 | 7 | 8 | 7 | 7 |
| Stearate | 18 | 8 | 9 | 8 | 8 |
Palmitate therefore gives 7 rounds and 8 acetyl-CoA, not 8 and 8. Getting this off by one is the most common error in the calculation.
Why Unsaturated Fatty Acids Yield Less
A double bond already present in the chain means the acyl-CoA dehydrogenase step — the one producing FADH2 — is skipped for that round. An isomerase repositions the existing bond instead.
| Fatty acid | Double bonds | FADH2 lost | ATP cost |
|---|---|---|---|
| Palmitate C16:0 | 0 | 0 | — |
| Oleate C18:1 | 1 | 1 | −1.5 |
| Linoleate C18:2 | 2 | 1 (plus NADPH cost) | −1.5 and more |
Each double bond costs roughly 1.5 ATP. Even-numbered double bonds cost more still, because they require an additional NADPH-consuming reductase step.
Why Fat Yields More ATP Per Carbon
Palmitate gives about 106 ATP from 16 carbons — roughly 6.6 per carbon — against glucose at about 32 ATP from 6 carbons, or 5.3 per carbon. The difference is oxidation state: fatty acid carbons are almost fully reduced, so more electrons are available to feed the electron transport chain.
Note the two-ATP activation cost. Attaching CoA consumes ATP but cleaves it to AMP rather than ADP, so it costs two high-energy phosphate bonds rather than one.
Worked Examples
Common Mistakes
Rounds equal (n/2) minus 1, because the last round produces two acetyl-CoA from a four-carbon fragment. Palmitate gives 7 rounds and 8 acetyl-CoA.
Attaching CoA cleaves ATP to AMP, costing two high-energy bonds rather than one. This must be subtracted from the total.
Each existing double bond skips the FADH2-producing step, costing about 1.5 ATP. Even-position bonds cost additionally through an NADPH-requiring reductase.
They end with propionyl-CoA rather than acetyl-CoA, which enters at succinyl-CoA and yields differently. It is also the one route by which fat carbon can reach gluconeogenesis.