FamilyTreeDNA (FTDNA) over-reports how much DNA is shared with matches. That’s because they include tiny segments of DNA in their totals. To determine how much DNA you really share with matches at FTDNA, you need to subtract segments under 7 cM. The reason this is needed is because you want to add up only segments that are identical by descent (IBD). These are larger and genealogically relevant. In contrast, segments that are smaller and most likely identical by state (IBS) are not genealogically relevant.
To do this,
- Click on box next to a match
- Then click on Chromosome Browser (CB) button
If there are few segments, just count them in the CB (excluding segments under 7 cM).
If there are many segments, click on Download to Excel (csv Format) button to download to a spreadsheet or look at them in a table. In the Excel spreadsheet (or table), subtract segments under 7 cM. Then add up the remaining segments to get a new total. This new total should then be used in the Shared cM Project Tool.