Calculate your DNA heritage percentage from your parents’ or grandparents’ ancestry, convert shared cM to percent, or see expected DNA shared by relatives.

Each parent passes on 50% on average and each grandparent 25%; DNA test results can differ from these expected shares.

Enter a mix like Irish 50, German 50. A name with no number gets the rest; blank counts as Unknown.

Blank ancestors
Optional mix used for every blank ancestor, e.g. English 100. Leave empty to count blanks as Unknown.

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 = (NX / Nₜₒₜₐₗ) × 100

Common composition summaries:

%GC = ((NG + NC) / Nₜₒₜₐₗ) × 100

For DNA, AT content is:

%AT = ((NA + NT) / Nₜₒₜₐₗ) × 100

For RNA, AU content is:

%AU = ((NA + NU) / Nₜₒₜₐₗ) × 100

Variables:

  • %X is the percentage of a specific nucleotide X (A, T/U, C, or G) (%)
  • NX is the count of nucleotide X in the sequence
  • Ntotal 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.

  1. Write down the DNA sequence and remove any spaces or line breaks.
  2. Count how many A, T, C, and G bases are present.
  3. Compute the total length Ntotal (in nucleotides, nt).
  4. Calculate each nucleotide percentage using %X = (NX / Ntotal) × 100.
  5. Optionally compute GC% = ((NG + NC) / Ntotal) × 100 and AT% = ((NA + NT) / Ntotal) × 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%