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Find Missing Numbers in a Sequence Online
Free online tool · No signup · Runs in your browser
Find missing integer ID ranges and duplicate IDs without generating enormous lists of missing numbers.
Your data stays in this browser tool. No account or upload to a processing service required.
Instructions
- Paste a table with a header and select the integer ID column.
- Generate the report.
- Gap rows show inclusive start and end IDs plus missing counts.
- Duplicate rows show the total number of occurrences of an ID.
Understanding your result
The sample IDs 100,102,102,105 have gaps 101 and 103–104, plus a repeated 102. Gap ranges are inclusive. These are gaps within observed endpoints, so the report cannot tell you whether an earlier or later ID should also exist.
What to do if you have a problem
If padded IDs merge, remember 00102 and 102 are the same numeric ID here. Blank IDs need correction before processing. A missing ID is a prompt to investigate the source sequence; deleted records or intentionally unused numbers can also explain a gap.
What to know before using the result
IDs must be whole numbers within JavaScript’s safe integer range, −9,007,199,254,740,991 to 9,007,199,254,740,991. Leading zeros and signs normalize to the same numeric ID. Reports only gaps between observed minimum and maximum IDs, never before or after them. Blank IDs are rejected. Gap counts use exact integer arithmetic. Input limit: 2 MB and 20,000 rows; output is capped at 20,000 report rows.
These tools work with pasted text or supported CSV files rather than Excel workbook files. CSV exports contain values and do not preserve workbook formatting, formulas or multiple worksheets. Formula builders produce formula text to use in Excel. Data processing runs in the browser tool.
Try an example
ID,Name 100,Ada 102,Sam 102,Lee 105,Jo
Summary
Investigate the reported missing ranges and repeated IDs within the observed sequence endpoints.