GEDCOM errors: broken links, duplicate IDs and impossible dates, and how to find them

A broken link in a GEDCOM file points to a person or family that is not in the file, a duplicate ID is one ID used by two records, and an impossible date is something like a death before a birth. Our free GEDCOM checker finds all three and shows each one with its line number, but it does not change them: they are questions only you can answer, in the program where you keep your tree.

Last checked: 7 October 2026. The checker is ours; what it does is described below exactly as it works.

A small example with all three

0 @I1@ INDI
1 NAME Jan /Peeters/
1 BIRT
2 DATE 12 MAR 1850
1 DEAT
2 DATE 3 JAN 1805        death before birth: probably 1905
1 FAMC @F9@              broken link: there is no 0 @F9@ FAM
0 @I1@ INDI              duplicate ID: @I1@ is already Jan
1 NAME Anna /Claes/

Checked on its own, this piece gives: Broken links: 1 (line 7), Duplicate IDs: 1 (lines 1 and 8), People died before they were born: 1 (line 6). After you correct it in your program, the same part of the file could look like this:

0 @I1@ INDI
1 NAME Jan /Peeters/
1 BIRT
2 DATE 12 MAR 1850
1 DEAT
2 DATE 3 JAN 1905
1 FAMC @F2@
0 @I2@ INDI
1 NAME Anna /Claes/

What each error means

Broken links

GEDCOM connects people and families with IDs between @ signs: a person points to the family they were born into with FAMC and to their own family with FAMS, and a family points to its members with HUSB, WIFE and CHIL. The 5.5.1 standard says a pointer implies that the record it points to exists in the file. When it does not, usually because something was deleted, programs drop the link or stop importing.

A related problem is a one-sided link: the person says they belong to a family, but the family does not list them, or the other way round. The checker reports those separately.

Duplicate IDs

Every record needs its own ID, and the 5.5.1 standard says it must be unique within the file. Duplicates mostly come from merging two files or editing by hand. A program reading the file keeps one of the two records, so a person can disappear and links can point to the wrong person.

Impossible dates

The checker compares the first birth date and the first death date of each person, and the birth dates of parents and children. It reports:

• people who died before they were born;
• children born before their father or mother;
• children born after their mother's death;
• parents younger than 12 at a child's birth (a warning, worth a second look);
• people more than 120 years between birth and death (a warning);
• people who are their own ancestor, a loop that breaks charts in most programs.

Approximate dates (ABT, EST, CAL) are too vague to prove anything and are left out. Dates written in a form GEDCOM does not know, such as 31.12.1850 instead of 31 DEC 1850, are listed as Dates programs do not understand.

How to find and fix them, step by step

1. Open the GEDCOM checker and choose your .ged file. It is checked in your browser and never uploaded.
2. Problems come first, then things to check, then notes. Click Show where under each one to see the line numbers, IDs and names (up to 50 examples per type).
3. Look the people up in your genealogy program by name or ID and correct them there: fix the year, link the person to the right family, or merge or separate the two people that share an ID.
4. Export a new GEDCOM file and check it again until the list is empty or only has things you have decided are right.

The checker's repaired file does not touch any of this. It fixes the form of the file (character set, header, line endings, empty lines, indentation, a missing header or end marker), so it is worth downloading if those were listed too.

Other ways to check a GEDCOM file

Way	Good for	Watch out for
Our free GEDCOM checker	Checking a file before you import it or send it on; line numbers; nothing to install	Reports, does not correct the content
Your own genealogy program	Correcting the errors where your tree lives	What it checks differs per program
Gramps (free desktop program)	Its tool Verify the Data runs tests such as death before birth, unborn father or mother, dead mother and old age at death; Check and Repair Database checks the database for integrity problems	You first have to import the whole file
A text editor	Searching for one ID, such as @F9@	Changing an ID by hand means checking every link to it

Related: garbled characters such as é in a GEDCOM file, gaps in your family tree and where to search next and how to export a GEDCOM file.

Sources

• The GEDCOM Standard, release 5.5.1 (character sets, line length, cross-reference IDs, dates): gedcom.io/specifications/ged551.pdf
• FamilySearch GEDCOM 7.0 specification (UTF-8 only, no CONC, GEDZIP): gedcom.io/specifications/FamilySearchGEDCOMv7.html
• Gramps source code, list of tools (Verify the Data, Check and Repair Database): github.com/gramps-project/gramps/blob/maintenance/gramps60/gramps/plugins/tool/tools.gpr.py
• Gramps source code, Verify the Data tool (tests such as death before birth, unborn mother, old age at death): github.com/gramps-project/gramps/blob/maintenance/gramps60/gramps/plugins/tool/verify.py