🧬 Autosomal DNA Inheritance Percentage by Generation Calculator

On average, the percentage of autosomal DNA you share with a direct ancestor halves with each generation back — 50% from a parent, 25% from a grandparent, and so on. Actual inherited percentages vary due to the randomness of recombination, especially for more distant ancestors.

Generations back

Each generation halves the expected share

You get half your autosomal DNA from each parent, and each of them got half of theirs from each of their parents. The tool lists every generation from 1 to the number you enter:

expected share at generation n = 100 / 2^n percent

1  50%      4  6.25%      7  0.7813%
2  25%      5  3.125%     8  0.3906%
3  12.5%    6  1.5625%   10  0.0977%

Enter 6 and the card reads 1.5625%, your expected share with one 4x great-grandparent. Across a test measuring about 6,800 cM that is roughly 106 cM. Values of 1% and above are listed to two decimals, smaller ones to four, and below 0.01% the tool switches to exponential notation.

Averages, not measurements

Only the parent figure is fixed. You inherit exactly half your autosomal DNA from each parent. From grandparents back, recombination decides which half of each parent's own DNA was passed on, so real percentages scatter around these numbers.
The scatter widens as the share shrinks. A grandparent percentage is usually close to 25%; a 5x great-grandparent's expected 0.78% can easily be double or half that in practice.
Zero is a real outcome. Past roughly seven generations you carry no detectable DNA at all from a good share of your documented ancestors, even though the paper trail is sound.

These figures describe direct ancestors on a line of descent. Cousins, aunts and nieces sit on side branches and do not follow this halving series; for those, use a shared cM chart instead.

Frequently asked questions

How much DNA do I share with a great-grandparent?

12.5% on average, which is generation 3. The real figure varies because your own parent passed on a random half of what they carried from that person.

Can I have inherited no DNA from a real ancestor?

Yes, and it is common further back. By the 6x great-grandparent level the expected share is under 0.4%, and plenty of those ancestors leave nothing measurable in any one descendant.

Does this tell me how much DNA I share with a cousin?

No. This is the ancestor line only. Two people descending from a shared couple each inherit an independent sample, so cousin sharing is a range rather than a halving step.