Free DNA tool

Free DNA Inheritance Calculator

A DNA inheritance calculator shows the average shared DNA percentage and centimorgan (cM) range between two relatives, helping you predict family relationships from AncestryDNA, 23andMe, MyHeritage, or other autosomal DNA test results.

Pick a relationship below to see the expected shared DNA percentage, the average centimorgans, and the typical range reported by the Shared cM Project.

shared DNA percentagecentimorgan charthow much DNA do cousins sharegenetic inheritance calculator

Inheritance breakdown

Each generation passes down half of its autosomal DNA, so the expected shared percentage halves with every step between two relatives and their shared ancestor.

~50% per generationTotal cM ~ 6,800Random recombination

Avg shared %

12.5%

Of total autosomal DNA

Avg centimorgans

866

Mid-point of the typical range

Typical cM range

396 - 1,397

From the Shared cM Project

What this means

First cousins share grandparents and average about 12.5% of their DNA, typically falling between 600 and 1,200 centimorgans.

Shared ancestor diagram

Both branches descend from the shared ancestor. The deeper the branch, the more recombination has shrunk the shared segments.

Shared grandparents
Shared grandparents

Left branch

Cousin A

2 gens down

Generation 1

Generation 1

Generation 2

Cousin A

Endpoint

Right branch

Cousin B

2 gens down

Generation 1

Generation 1

Generation 2

Cousin B

Endpoint

DNA Inheritance Reference Chart

Average shared DNA percentage and centimorgan totals for the most common relationships, drawn from the Shared cM Project 4.0 (Bettinger, 2020).

RelationshipAvg shared DNAAvg cMTypical cM range
100%6,800 cM6,701 - 7,100 cM
50%3,485 cM2,376 - 3,720 cM
50%2,613 cM1,613 - 3,488 cM
25%1,759 cM1,160 - 2,436 cM
25%1,766 cM1,156 - 2,311 cM
25%1,750 cM1,201 - 2,282 cM
12.5%881 cM464 - 1,486 cM
12.5%866 cM396 - 1,397 cM
12.5%871 cM492 - 1,315 cM
12.5%914 cM251 - 2,108 cM
6.25%433 cM102 - 980 cM
6.25%449 cM156 - 979 cM
3.13%229 cM41 - 592 cM
3.13%221 cM43 - 531 cM
1.5%122 cM14 - 353 cM
0.78%73 cM0 - 234 cM
0.39%48 cM0 - 192 cM
0.20%35 cM0 - 127 cM

How DNA inheritance works

Every person inherits exactly half of their autosomal DNA from each parent, but the specific segments are randomly mixed during a process called recombination. That is why siblings, even though they share the same parents, can have noticeably different DNA matches with the same cousin.

With each generation, the expected shared DNA between relatives roughly halves. You share 50% with a parent, 25% with a grandparent, 12.5% with a great-grandparent, and so on. The same logic applies sideways to cousins: first cousins average 12.5%, second cousins about 3.13%, and third cousins less than 1%.

Centimorgans (cM) measure the length of shared DNA segments based on how often they get inherited intact. A higher total cM means a more recent common ancestor. Companies like AncestryDNA, 23andMe, and MyHeritage report total shared cM as the most reliable signal of how closely two people are related.

Because each generation reshuffles the deck, the actual shared DNA can vary widely. Two third cousins might share 130 cM or zero. Always use the typical range, not just the average, when interpreting a real DNA match.

DNA inheritance calculator FAQ

Direct answers to the questions people ask most when looking up a DNA match or shared centimorgan total.

How much DNA do first cousins share?

First cousins share an average of 12.5% of their DNA, which is about 866 centimorgans. The typical range is between 396 and 1,397 cM because each generation passes down a random subset of DNA segments.

What are centimorgans?

A centimorgan (cM) is a unit that measures the length of a shared DNA segment based on how often it gets passed down without being broken up by recombination. Companies like AncestryDNA, 23andMe, and MyHeritage report total shared cM as the main signal of how closely two people are related.

Why do siblings share different amounts of DNA?

Siblings each inherit a random 50% mix of DNA from each parent, but the specific segments differ. That is why full siblings can share anywhere from about 1,613 to 3,488 cM even though the average is 2,613 cM, or roughly 50%.

How accurate is shared DNA for predicting a relationship?

Shared DNA narrows the possibilities but rarely identifies a single relationship on its own. Many ranges overlap; for example, a 25% match could mean a half sibling, grandparent, or aunt or uncle. Combine the cM total with age, family stories, and a documented tree to confirm the connection.

Can shared DNA tell me my exact relationship?

Not always. The Shared cM Project shows that most cM totals are consistent with several possible relationships. Tools like this calculator give you the average and range; pair them with known birth years, parent matches, and chromosome browser data to pick the most likely option.