ICD-10 Conversion and Mapping

ICD Code Translator


The below tutorial explains ICD-9 to ICD-10 conversion and mapping. For help with converting codes, refer to our online ICD-10 code conversion tool, see our ICD-9 to ICD-10 crosswalks by specialty, or consider our ICD-10 mapping services.

One of the identified benefits for the United States' transition from ICD-9 to ICD-10 is because of the increased level of specificity offered by the ICD-10 code format. This specificity will benefit patients and doctors (by giving more detailed diagnosis and treatment information), payers (by more accurately defining services) and international organizations that monitor worldwide disease.

However, all of this increased specificity comes at a price—the codes are becoming more complex. In ICD-9-CM, codes are three to five digits. The first digit is either numeric or alpha (the letters E or V only) and all other digits are numeric.

ICD-9-CM code format

In ICD-10-CM, however, codes can be up to seven digits. The first digit is always alpha (it can be any letter except U), the second digit is always numeric, and the remaining five digits can be any combination.

ICD-10-CM code format

The following example shows an ICD-10-CM code for chronic gout due to renal impairment, left shoulder, without tophus.

Example of ICD-10-CM code

The corresponding ICD-9-CM code would have been 274.02, which only indicates gouty arthropathy. As you can see, the ICD-10-CM code contains much more information.


Some ICD-9-CM codes map easily to ICD-10 in a simple one-to-one conversion. For example, the ICD-9-CM code 733.6 (Tietze's Syndrome) maps directly to the ICD-10-CM code M94.0. (An exact map does not always mean the codes match in detail.)

1 to 1 mapping

Other codes will require additional information to map for possible solutions. For example, the ICD-9-CM code 649.51 (spotting complicating pregnancy) requires information about weeks in pregnancy to map. There are three options: O26.851 (spotting complicating pregnancy, first trimester), O26.852 (spotting complicating pregnancy, second trimester), and O26.853 (spotting complicating pregnancy, third trimester).

1 to 3 mapping

And some codes require significantly more specificity and map into many more ICD-10-CM code set selections. For example, the ICD-9-CM code 962.9 (poisoning by hormones and synthetic substitutes) has sixteen corresponding ICD-10-CM codes, requiring information about both the cause of the poisoning and the type of encounter.

1 to 16 mapping

In an extreme example, the ICD-9-CM code 733.82 (other disorders of bone and cartilage, nonunion of fracture) there are 2530 corresponding ICD-10-CM codes due to the degree of specificity required in ICD-10.

1 to 2350 mapping

Last Reviewed on Jan 16, 2020 by AAPC Thought Leadership Team