Dna Percentage Calculator

Calculate DNA percentages from ancestor mixes, shared cM, or common-ancestor steps to estimate relationship matches and heritage shares for genealogy research.

Enter values, then click Calculate.

Heritage Mix

Shared DNA

Ancestor Share

Heritage Mix From Ancestors

Ancestor level Default for blank ancestors

Ancestor 1

Ancestor 2

Ancestor 3

Ancestor 4

Ancestor 5

Ancestor 6

Ancestor 7

Ancestor 8

Shared DNA Percentage And cM

Shared DNA

Total autosomal DNA scale

Expected DNA From A Common Ancestor

Relationship preset Person A steps to common ancestor

Person B steps to common ancestor

Shared common ancestors

Show Calculation Steps ▼

Related Calculators

DNA Nucleotide Percentage Formula

The following formulas are used to calculate nucleotide percentages (base composition) within a single DNA (or RNA) sequence.

\%X = (N_X / N_{total}) * 100

Common composition summaries:

\%GC = ((N_G + N_C) / N_{total}) * 100

For DNA, AT content is:

\%AT = ((N_A + N_T) / N_{total}) * 100

For RNA, AU content is:

\%AU = ((N_A + N_U) / N_{total}) * 100

Variables:

%X is the percentage of a specific nucleotide X (A, T/U, C, or G) (%)
N_X is the count of nucleotide X in the sequence
N_total is the total number of nucleotides in the sequence (sequence length, in nt)

To calculate a nucleotide percentage, divide the count of that nucleotide by the total sequence length, then multiply by 100. GC%, AT%, and AU% are calculated the same way using the combined counts.

What is a DNA Percentage?

On this page, “DNA percentage” refers to base composition: the percentage of each nucleotide (A, T, C, and G) present in a DNA sequence, along with summary measures like GC content (G+C) and AT content (A+T). These percentages describe a sequence itself (or windows within a sequence), not how much DNA two people share. Shared-DNA percentages used in ancestry/relationship testing come from population genetics methods and are a different concept.

How to Calculate DNA Percentage?

The following steps outline how to calculate nucleotide percentages (base composition) for a DNA sequence.

Write down the DNA sequence and remove any spaces or line breaks.
Count how many A, T, C, and G bases are present.
Compute the total length N_total (in nucleotides, nt).
Calculate each nucleotide percentage using %X = (N_X / N_total) × 100.
Optionally compute GC% = ((N_G + N_C) / N_total) × 100 and AT% = ((N_A + N_T) / N_total) × 100.

Example Problem:

Use the following variables as an example problem to test your knowledge.

DNA sequence = ATGCGCATTAACGTTAGC (18 nt)

A = 5 (27.78%), T = 5 (27.78%), C = 4 (22.22%), G = 4 (22.22%), GC% = 44.44%