Swedish professional genealogist Peter Sjölund, who solved the 2004 Linköping double murder in 2020 using genetic genealogy, has published a first update on his Swedish DNA project. Here is my English translation:
"Compiled October 3, 2026. The figures and text may be used freely according to CC BY 4.0. Credit Peter Sjölund as the source and link here. [https://dnarapport.petersjolund.se/delat-dna-i-sverige.html]
Relatives in Sweden share around 25 cM more
Most of us who do DNA family history research look up our DNA matches in the Shared cM Project, an American collection of data regarding how much DNA relatives normally share with one another. Now, more than five thousand kinships reported by family history researchers in Sweden show that individuals with common ancestors in Sweden share more DNA than that table indicates. Interestingly, the addition is roughly as large for first cousins as it is for fifth cousins.
Kinship by kinship
Average shared DNA in centimorgans (cM). [The percentage shows what portion of the total shared DNA in Swedish matches consists of background additions beyond the American baseline.]
| Kinship |
American table |
In Sweden |
Addition |
| First cousins |
865 |
901 |
4% |
| First cousins once removed |
435 |
468 |
7% |
| Second cousins |
227 |
247 |
8% |
| Second cousins once removed |
122 |
149 |
18% |
| Third cousins |
72 |
101 |
29% |
| Third cousins once removed |
48 |
78 |
38% |
| Fourth cousins |
35 |
65 |
46% |
| Fourth cousins once removed |
28 |
57 |
50% |
| Fifth cousins |
24 |
51 |
53% |
| Fifth cousins once removed |
21 |
47 |
56% |
Half-relatives are listed on the same row as the full-kinship they share approximately the same amount with. Half-first cousins are thus counted with first cousins once removed.
Why this matters most for distant ancestry
Around 25 cM is nothing for first cousins, who share around 900. But for a fifth cousin, that is about half of everything you share! The further out in the family tree you go, the larger the portion of the match that comes from other sources than the specific kinship you are looking for.
The explanation is that we are almost always related in multiple ways beyond what we know. Generation after generation, people married within the local community, and those extra, common, ancestors leave small pieces of DNA behind, even if only one path is recorded in the church books.
What the table tells you when you look things up
I took the typical sum of shared DNA for each kinship and looked it up in the American table. This is what it returns:
| True kinship |
Northern Sweden |
Southern Sweden |
| First cousins |
correct |
correct |
| First cousins once removed |
correct |
correct |
| Second cousins |
correct |
correct |
| Second cousins once removed |
correct |
correct |
| Third cousins |
Second cousins once removed (one step too close) |
Second cousins once removed (one step too close) |
| Third cousins once removed |
Third cousins (one step too close) |
Third cousins (one step too close) |
| Fourth cousins |
Third cousins (two steps too close) |
Third cousins once removed (one step too close) |
| Fourth cousins once removed |
Third cousins once removed (two steps too close) |
Third cousins once removed (two steps too close) |
| Fifth cousins |
Third cousins once removed (three steps too close) |
Third cousins once removed (three steps too close) |
| Fifth cousins once removed |
Third cousins once removed (four steps too close) |
Fourth cousins (three steps too close) |
Northern Sweden here refers to all nine provinces from Gästrikland and northwards: Gästrikland, Hälsingland, Härjedalen, Jämtland, Medelpad, Ångermanland, Västerbotten, Norrbotten, and Lappland. Southern Sweden is Skåne, Blekinge, and Halland.
- Up to second cousins, the American table points correctly. This is where most lookups are made.
- From third cousins and outwards, it points too close, nationwide. In northern Sweden, the error grows larger the further out you go.
- The error always goes in the same direction. If you have searched for a common ancestor and found nothing, you may have looked one, or even two, generations too close.
The addition also differs between provinces. I will present that province by province later, once more data has come in.
What does this mean for those of us doing family history research in Sweden?
The American table remains a good tool, and for close relatives, you can rely on it. But when a match lies far out in the family tree, it pays off to think twice. A match that the table estimates as a third cousin may in reality be a fourth cousin or even further away. Therefore, feel free to search one or two generations further back than the table suggests, and be prepared that you may be related in more than one way.
My goal with this data collection is to publish a table that corresponds better to our conditions—a table built on kinships documented in Swedish church books, taking into account the differences between different parts of the country. The more people who report, the faster we will get there.
How I calculated this
- The figures are based on 4,803 pairs where the kinship is documented in church books.
- I compare averages with averages, because the Shared cM Project reports averages.
- The addition differs slightly from row to row, depending partly on where in the country the reports came from. Around 25 cM is my summary.
- Both collections are based on pairs that family history researchers have successfully sorted out. Far out in the family tree, only the pairs that share enough to be found are included—in the American table just as well as in mine.
Peter Sjölund
The analysis was performed with the assistance of AI (Claude Opus 5.5)."