Glycolysis ( Net ATP and NADH )

Biology • Cellular Energy and Metabolism

Written by STEM Calculators Team Published January 6, 2026 Updated February 24, 2026

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Anaerobic context note

This calculator summarizes the net yields of glycolysis. Under anaerobic conditions, the net ATP stays 2 per glucose; fermentation mainly reoxidizes NADH back to NAD⁺ so glycolysis can continue.

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Glycolysis yield: net ATP, NADH, and pyruvate

Glycolysis is a central metabolic pathway that breaks down one glucose molecule (6 carbons) into two pyruvate molecules (3 carbons each). It occurs in the cytosol of both eukaryotic and prokaryotic cells and produces energy primarily as ATP (substrate-level phosphorylation) and NADH (reduced electron carrier).

Energy logic: investment phase vs payoff phase

Glycolysis is commonly divided into two functional phases:

Energy investment phase: ATP is consumed to phosphorylate and “prime” glucose.
Energy payoff phase: ATP is produced and NAD⁺ is reduced to NADH.

Key yields per glucose

The standard textbook accounting for one glucose is:

Quantity (per 1 glucose)	Amount	Where it comes from
ATP invested	2	Hexokinase (HK) and phosphofructokinase-1 (PFK-1)
ATP produced	4	Phosphoglycerate kinase (PGK) and pyruvate kinase (PK) occur twice per glucose
Net ATP	2	ATP produced − ATP invested
NADH produced	2	Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) occurs twice per glucose
Pyruvate produced	2	One glucose splits into two 3-carbon end products

Net ATP calculation

Net ATP is the difference between ATP formed in the payoff phase and ATP consumed in the investment phase.

\[ \begin{aligned} \text{ATP}_{\text{net}} &= \text{ATP}_{\text{produced}} - \text{ATP}_{\text{invested}} \\ &= 4 - 2 \\ &= 2 \end{aligned} \]

Overall glycolysis reaction (summary form)

A common overall summary for glycolysis (details may vary slightly by convention) is:

\[ \begin{aligned} \text{Glucose} + 2\,\text{NAD}^{+} + 2\,\text{ADP} + 2\,\text{P}_{\text{i}} \rightarrow 2\,\text{Pyruvate} + 2\,\text{NADH} + 2\,\text{H}^{+} + 2\,\text{ATP} + 2\,\text{H}_{2}\text{O} \end{aligned} \]

Scaling yields to any glucose amount

If you have an amount of glucose expressed in moles, the totals scale linearly because the stoichiometric coefficients are “per glucose.” Let n_glc be the amount of glucose in moles.

\[ \begin{aligned} \text{ATP}_{\text{invest}} &= 2 \cdot n_{\text{glc}} \\ \text{ATP}_{\text{produced}} &= 4 \cdot n_{\text{glc}} \\ \text{ATP}_{\text{net}} &= 2 \cdot n_{\text{glc}} \\ \text{NADH} &= 2 \cdot n_{\text{glc}} \\ \text{Pyruvate} &= 2 \cdot n_{\text{glc}} \end{aligned} \]

If glucose is provided in grams, convert mass to moles using the molar mass of glucose: \( M_{\text{glc}} = 180.156\ \mathrm{g \cdot mol^{-1}} \).

\[ \begin{aligned} n_{\text{glc}} &= \frac{m_{\text{glc}}}{M_{\text{glc}}} \end{aligned} \]

Anaerobic note: why net ATP stays 2

Under anaerobic conditions (limited oxygen), glycolysis can still produce 2 net ATP per glucose because ATP formation in glycolysis does not require oxygen directly. The key limitation is that glycolysis needs a supply of NAD⁺. Since glycolysis produces NADH, cells must reoxidize NADH back to NAD⁺.

In many tissues (and many microbes), fermentation pathways regenerate NAD⁺ (e.g., lactate fermentation).
This regeneration step allows glycolysis to continue, but typically does not add extra ATP beyond glycolysis’ net 2 ATP.

Organism context (eukaryote vs prokaryote)

The glycolysis pathway and its net yields per glucose are the same in typical eukaryotes and prokaryotes. The main differences appear after glycolysis (pyruvate processing, electron transport, and how cytosolic NADH is handled in eukaryotes). That’s why this calculator’s eukaryote/prokaryote option mainly adjusts wording rather than the core yields.

Tip: Use “per 1 glucose” mode when you want the fixed textbook yields. Use “scaled totals” when you want totals for a measured amount of glucose (mol or grams).

Frequently Asked Questions

What are the net products of glycolysis per 1 glucose?

In standard textbook accounting, glycolysis yields 2 net ATP, 2 NADH, and 2 pyruvate per glucose. This comes from 2 ATP invested and 4 ATP produced, giving net ATP = 4 - 2 = 2.

How does the calculator compute net ATP in glycolysis?

It uses net ATP = ATP produced - ATP invested. When the ATP breakdown option is enabled, it shows the investment and payoff totals used to form the net.

How are glycolysis yields scaled for a glucose amount in moles or grams?

Totals scale linearly with the moles of glucose: each yield coefficient is multiplied by n_glc. If glucose is entered in grams, the calculator converts to moles using n_glc = m_glc / M_glc before scaling.

Does glycolysis still produce 2 net ATP without oxygen?

Yes, the net ATP from glycolysis remains 2 per glucose under anaerobic conditions. The main issue is regenerating NAD+ from NADH so glycolysis can continue, which is why fermentation is often discussed alongside glycolysis.

Why does the calculator include an eukaryote vs prokaryote option if yields are the same?

The glycolysis pathway and its net yields per glucose are the same in typical eukaryotes and prokaryotes. The option provides organism context for interpretation, while the core glycolysis yields remain unchanged.

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