Glycolysis ATP Calculator

Calculate net ATP, NADH, and pyruvate yield from glycolysis of glucose.

Moles of glucose (mol)

Starting substrate

Route

Aerobic or anaerobic context

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Where the Numbers Come From

Glycolysis spends two ATP in the investment phase and produces four in the payoff phase, giving a net of two per glucose. It also generates two NADH, whose eventual yield depends on how they reach the mitochondrion.

Stage	ATP	NADH	Note
Investment phase	−2	—	Hexokinase and PFK-1
Payoff phase	+4	+2	Two three-carbon units
Net glycolysis	+2	+2	Cytoplasmic
From glycogen	+3	+2	One ATP saved — G6P already phosphorylated

The glycogen route is more efficient precisely because glucose-6-phosphate arrives already phosphorylated, skipping the hexokinase step that would consume an ATP.

Why Total Yield Figures Disagree

Textbooks quote 30, 32, 36 or 38 ATP per glucose, and the disagreement is real rather than sloppiness. Three things vary:

Variable	Options	Effect
P/O ratios	2.5 or 3 per NADH	Older texts use whole numbers
Shuttle used	Malate–aspartate or glycerol phosphate	2.5 or 1.5 per cytosolic NADH
Transport costs	Counted or ignored	Moving ATP out costs energy

The shuttle difference is tissue-specific and real. Heart and liver use the malate–aspartate shuttle, delivering cytosolic NADH as mitochondrial NADH worth 2.5 ATP. Skeletal muscle and brain use the glycerol phosphate shuttle, which delivers to FADH₂ instead, worth only 1.5. The same glucose yields different ATP in different tissues.

Modern consensus favours about 30–32 ATP per glucose, with the older figure of 38 reflecting whole-number P/O ratios that measurement has since refined.

Anaerobic Glycolysis and the Warburg Effect

Without oxygen, NADH cannot be reoxidised by the electron transport chain, so pyruvate is reduced to lactate instead. That regenerates NAD⁺ and allows glycolysis to continue — yielding only 2 ATP, but rapidly.

Many tumours run glycolysis to lactate even with oxygen present, the Warburg effect. Despite being far less efficient per glucose, glycolysis produces ATP faster and supplies carbon intermediates for building biomass, which a rapidly dividing cell needs more than efficiency.

Worked Examples

Example 1: 1 glucose, aerobic

Net 2 ATP in glycolysis alone

Result: Plus 5 ATP from cytoplasmic NADH = 7 total from glycolytic phase

TCA and OXPHOS add remaining 23 ATP

Example 2: Glucose-6-phosphate (from glycogen)

Net 3 ATP (save 1 ATP vs free glucose)

Result: Glycogen mobilization more ATP-efficient

Liver/muscle glycogen directly enters at G6P

Example 3: Tissue-dependent yield

Same glucose in heart versus skeletal muscle

Result: 32 versus 30 ATP

The malate–aspartate shuttle in heart delivers cytosolic NADH worth 2.5 ATP each; the glycerol phosphate shuttle in muscle delivers 1.5. Two NADH means a two-ATP difference.

Example 4: Why tumours use glycolysis

Aerobic glycolysis to lactate, 2 ATP per glucose

Result: Faster ATP production plus biosynthetic carbon

Oxidative phosphorylation is more efficient but slower. A dividing cell needs building blocks and rapid ATP more than it needs maximum yield per glucose.

Common Mistakes

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Quoting a single total ATP figure

Yield depends on which shuttle the tissue uses and which P/O ratios are assumed. Heart and skeletal muscle genuinely differ.

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Forgetting glycolysis produces two three-carbon units

Everything after the aldolase step happens twice per glucose. Counting the payoff phase once halves the answer.

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Assuming anaerobic glycolysis is simply inefficient

It is far less efficient per glucose but faster per unit time, and it supplies biosynthetic intermediates. That is why proliferating cells use it even with oxygen available.

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Using 38 ATP as the modern figure

That assumes whole-number P/O ratios. Measured values give about 2.5 ATP per NADH and 1.5 per FADH₂, so 30–32 is the current consensus.

Frequently Asked Questions

Warburg effect?

Cancer cells use aerobic glycolysis (glucose→lactate even with O2). Less efficient (2 vs 30 ATP) but faster rate + biosynthetic precursors. PET scans detect high 18F-FDG uptake in tumors.

Key regulatory enzyme?

Phosphofructokinase-1 (PFK-1): rate-limiting step. Inhibited by high ATP, citrate. Activated by AMP, fructose-2,6-bisphosphate (key regulator linking insulin/glucagon signaling to glycolysis rate).

How much ATP does glycolysis produce?

Two net per glucose, plus two NADH. From glycogen it is three, because glucose-6-phosphate skips the hexokinase step.

Why do textbooks disagree on total ATP yield?

Because P/O ratios and shuttle systems differ. Modern consensus is 30–32; the older 38 assumed whole-number P/O ratios.

Why does the shuttle matter?

The malate–aspartate shuttle delivers cytosolic NADH worth 2.5 ATP, while the glycerol phosphate shuttle delivers to FADH₂ worth 1.5. Tissues differ in which they use.

What is the Warburg effect?

Tumour cells running glycolysis to lactate even with oxygen present. It is less efficient per glucose but produces ATP faster and supplies biosynthetic intermediates.