Shared cM relationship calculator.
Enter the total centimorgans shared with a DNA match to see which genealogical relationships fit the reported ranges—and where the number alone stops being informative.
“I share 275 cM with this person. How might we be related?”
A total such as 275 cM can fit second cousin, half second cousin, first cousin twice removed, second cousin once removed, and other relationships. The overlap is real: autosomal DNA is inherited randomly, so the total narrows a family-tree search but does not finish it.
What do common shared-cM totals mean?
Each amount crosses several relationship distributions. These examples describe the search space without turning one number into one relationship.
50 cMUsually a distant relationship with many possibilities
This amount fits numerous cousin relationships. Shared matches and family trees usually provide more discrimination than the total alone.
100 cMSeveral cousin paths still overlap
Relationships around the second- to third-cousin level and removed or half relationships can all fall near this amount.
200 cMOften a useful recent-family clue
Second cousin, first cousin twice removed, half-cousin and other asymmetric relationships can overlap around 200 cM.
500 cMCloser relationships become more prominent
First cousin once removed, half first cousin, second cousin and great-aunt or great-uncle paths may all remain possible.
1,000 cMA close relative, but not one unique answer
First cousin, first cousin once removed, great-grandparent and some half relationships approach or include this amount.
Why the answer is not exact.
- Autosomal DNA is inherited randomly, so known relatives can share different totals.
- Endogamy, pedigree collapse, or more than one relationship can inflate or broaden shared DNA.
- Distant genealogical relatives may share no detectable DNA at all.
- Testing services use different matching and segment-reporting methods.
- Ages can constrain direction, but trees and shared-match evidence are needed to establish a relationship.
Shared cM Project 4.0.
Relationship ranges and averages are adapted from Blaine T. Bettinger's Shared cM Project 4.0 under the CC BY 4.0 licence. The project analysed 55,418 curated submissions after outlier removal. Displayed ranges are the project's trimmed 99th-percentile reported ranges, not hard biological boundaries.
For relationships more distant than half second cousin, reported averages include only submissions in which detectable DNA was shared.
Read the source reportShared cM calculator FAQ.
Can shared cM identify one exact relationship?
No. Relationship ranges overlap, sometimes substantially. The result is a set of hypotheses for further genealogical research.
Why might an age conflict appear?
Direct relationships have a required direction: a parent must be older than a child. The flag checks that ordering only. It does not score cousin relationships or uncommon age gaps.
Does this analyse my raw DNA?
No. This calculator uses only the total cM and optional ages you enter. The separate ancestry modules accept supported raw DNA exports.