Guidance
Alcohol back calculation for road traffic investigations
Guidance on the reporting of alcohol back calculation cases where the time between the reported last drink and the incident of interest is less than 1 hour.
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Back calculation is the process whereby a forensic toxicologist uses the concentration of alcohol in a blood or breath sample to calculate the concentration of alcohol in the individual’s blood or breath at some time before the sample was taken. This type of evidence appears regularly in road traffic investigations.
You can view the previous version of this guidance on the national archives.
Updates to this page
Published 8 May 2015
Last updated 22 September 2020 + show all updates
Last updated 22 September 2020 + show all updates
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Updated guidance.
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First published.