PDCAAS Calculator

Enter your amino acid score and true digestibility — or pick a common protein source preset — to calculate PDCAAS and see a full quality breakdown.

Created by Luis GonzalezLast updated: May 9, 2026

How to Use This Calculator

1
Enter the AA Score (%)
Input the limiting amino acid score as a percentage. Values over 100% are typically truncated to 100% for the final PDCAAS score.
2
Specify True Digestibility (%)
Enter the true fecal digestibility of the protein, usually ranging from 80% to 99%. Higher values indicate better absorption.
3
Select a Protein Source Preset
Choose a common protein source (e.g., Egg, Whey, Soy) to auto-fill typical AA Score and Digestibility values, or select 'Custom'.
4
Review your results
The calculator will display the PDCAAS score, digestible protein percentage, and other protein quality metrics.

Example Calculation

A food scientist wants to determine the protein quality of a new ingredient with a known amino acid score and digestibility, using the PDCAAS method.

AA Score (%)

100

True Digestibility (%)

Protein Source Preset

Custom

Results

0.95

Tips

Understand the Limiting Amino Acid

The AA Score is determined by the 'limiting amino acid'—the essential amino acid present in the lowest proportion compared to a reference standard. This single amino acid dictates the overall protein quality.

Consider Processing Impact on Digestibility

Protein processing methods (e.g., heating, fermentation) can significantly alter true digestibility. Always use digestibility data specific to the processed form of the protein, not just the raw ingredient.

Compare with the Egg Standard

Whole egg protein has a PDCAAS of 1.0, making it the benchmark for complete protein. Compare your calculated PDCAAS to egg to gauge its relative biological value for human nutrition.

Understanding Protein Quality with the PDCAAS Calculator

The PDCAAS Calculator allows you to instantly assess the quality of a protein based on its amino acid score and true digestibility. PDCAAS (Protein Digestibility-Corrected Amino Acid Score) is a widely recognized method, adopted by the FAO/WHO, for evaluating how well a protein meets human nutritional needs. A score of 1.0, like that of whole egg protein, signifies a complete, high-quality protein, while scores can range down to 0 for incomplete proteins. This tool helps in understanding the nutritional value of various protein sources for dietary planning and food product development.

Why Protein Quality is a Key Nutritional Metric

Protein quality is a fundamental nutritional metric because not all proteins are created equal in their ability to support human health. Proteins are made of amino acids, nine of which are essential and must be obtained from the diet. A high-quality protein provides all essential amino acids in proportions that meet the body's needs for growth, repair, and maintenance. Low-quality proteins, lacking sufficient amounts of one or more essential amino acids, can limit the body's ability to synthesize new proteins, even if total protein intake is adequate. This distinction is crucial for diet planning, especially for vegetarians, vegans, and those with specific dietary requirements.

Calculating Protein Quality: The PDCAAS Formula Explained

The PDCAAS (Protein Digestibility-Corrected Amino Acid Score) is calculated by multiplying a protein's limiting amino acid score by its true fecal digestibility. The result is then truncated to a maximum value of 1.0.

Here's the breakdown of the calculation:

Amino Acid (AA) Score: This is the ratio (as a percentage) of the first limiting essential amino acid in the test protein to the same amino acid in a reference protein pattern.
- Example: If a protein has only 80% of the required lysine compared to the reference, its AA Score is 80%.
True Digestibility: This measures the proportion of protein that is actually absorbed by the body.

Raw PDCAAS Calculation:

Raw PDCAAS = (AA Score / 100) × (True Digestibility / 100)

Final PDCAAS: The raw PDCAAS is then truncated, meaning any value greater than 1.0 is capped at 1.0.
```
PDCAAS = MIN(1.0, Raw PDCAAS)
```

💡 For a broader understanding of body composition and dietary needs, our Lean Body Weight Calculator can help estimate your non-fat mass, which influences protein requirements.

Determining the PDCAAS for a Standard Protein Source

Let's calculate the PDCAAS for a protein with an amino acid score of 100% and a true digestibility of 95%. This scenario is common for high-quality proteins like whey or egg.

Convert AA Score to Decimal: 100% / 100 = 1.0.
Convert True Digestibility to Decimal: 95% / 100 = 0.95.
Calculate Raw PDCAAS: Multiply the decimal AA Score by the decimal True Digestibility: 1.0 × 0.95 = 0.95.
Apply Truncation: Since 0.95 is not greater than 1.0, the value is not truncated.

The final PDCAAS for this protein is 0.95. This indicates a very high-quality protein, nearly matching the ideal score of 1.0, meaning it provides an excellent balance of essential amino acids that are well-absorbed by the body.

💡 Planning meals and understanding nutrient distribution can be complex; our Leftover Portion Calculator can assist in managing food quantities efficiently.

Nutritional Implications of Protein Quality

The quality of protein consumed has significant nutritional implications, particularly for muscle synthesis, immune function, and overall metabolic health. According to the FAO/WHO, a protein with a PDCAAS of 1.0 provides 100% of the essential amino acids required for growth and maintenance, making it highly effective. Conversely, proteins with lower scores, such as many plant-based proteins (e.g., rice protein might be 0.40-0.50), may require careful dietary planning to ensure adequate intake of all essential amino acids through complementary protein sources. For instance, combining legumes with grains can provide a complete amino acid profile, despite each being individually incomplete.

When PDCAAS May Not Be the Best Measure of Protein Quality

While PDCAAS has been widely used, there are specific scenarios where it might provide misleading or incomplete information about protein quality. One major limitation is the truncation effect, where any score above 1.0 is rounded down to 1.0. This means that a protein that significantly exceeds amino acid requirements and has high digestibility (e.g., whey protein, which might have a raw score of 1.1 or higher) still receives the same score as a protein that just barely meets the 1.0 threshold (e.g., casein). This truncation prevents differentiation between truly superior protein sources.

Additionally, PDCAAS relies on fecal digestibility, which can overestimate the amount of amino acids actually absorbed and available for metabolic use. Amino acids that reach the large intestine and are fermented by gut bacteria are not absorbed by the body, but fecal digestibility methods don't fully account for this. For these reasons, the FAO has recommended shifting towards the Digestible Indispensable Amino Acid Score (DIAAS), which uses ileal digestibility (measured at the end of the small intestine) and does not truncate scores, offering a more precise and accurate assessment, particularly for individual food ingredients. Therefore, for highly precise nutritional analyses or comparisons of top-tier protein supplements, relying solely on PDCAAS may not be sufficient.

Frequently Asked Questions

What is PDCAAS and why is it used?

PDCAAS stands for Protein Digestibility-Corrected Amino Acid Score, a method adopted by FAO/WHO in 1991 to evaluate protein quality based on human nutritional requirements. It measures how well a protein's amino acid profile meets human needs, corrected for its digestibility. A score of 1.0 indicates a complete protein that provides 100% or more of the essential amino acids per unit of protein, after digestion, like casein or egg white. It's widely used in food labeling and dietary recommendations.

How is the 'AA Score' determined in PDCAAS?

The Amino Acid (AA) Score in PDCAAS is determined by comparing the amount of the most limiting essential amino acid in a test protein to the amount of the same amino acid in a high-quality reference protein pattern (typically based on human amino acid requirements). The limiting amino acid is the one present in the lowest quantity relative to the reference. For example, if a protein has only 80% of the required lysine, its AA Score for lysine is 80%, and this becomes the overall AA Score if lysine is the most limiting amino acid.

What does 'True Digestibility' mean for protein quality?

True digestibility in the context of PDCAAS refers to the proportion of ingested protein that is absorbed by the body, after accounting for endogenous fecal protein losses. It's typically measured in animal studies (e.g., rats or pigs) and reflects how much of the protein's amino acids are actually available for use by the body. A higher true digestibility, often 90-99% for animal proteins, means more of the amino acids are absorbed, leading to a higher overall protein quality score.

What is the maximum possible PDCAAS score?

The maximum possible PDCAAS score is 1.0. Even if a protein's raw score (Amino Acid Score multiplied by True Digestibility) calculates to a value greater than 1.0, it is truncated to 1.0. This truncation reflects the understanding that once a protein provides 100% of the essential amino acids needed by the body, corrected for digestibility, any excess amino acids do not further enhance its quality for human nutritional purposes according to this specific scoring method.

How does PDCAAS compare to DIAAS?

PDCAAS has been widely used but has limitations, such as the truncation of scores to 1.0 and its reliance on fecal digestibility, which can overestimate protein quality. The Digestible Indispensable Amino Acid Score (DIAAS) is a newer, preferred method recommended by the FAO, which addresses these issues by using ileal digestibility (measured at the end of the small intestine) and does not truncate scores. DIAAS provides a more accurate and sensitive measure of protein quality, especially for individual food ingredients.