diff --git a/.github/pull_request_template.md b/.github/pull_request_template.md
index 68a6e692a46..958cc21fdd4 100644
--- a/.github/pull_request_template.md
+++ b/.github/pull_request_template.md
@@ -13,7 +13,7 @@ Fixes # (issue)
 # Checklist
 
 - [ ] I have performed a self-review of my own code
-- [ ] I have run [clang-format](https://docs.openmc.org/en/latest/devguide/styleguide.html#automatic-formatting) (version 15) on any C++ source files (if applicable)
+- [ ] I have run [clang-format](https://docs.openmc.org/en/latest/devguide/styleguide.html#automatic-formatting) (version 18) on any C++ source files (if applicable)
 - [ ] I have followed the [style guidelines](https://docs.openmc.org/en/latest/devguide/styleguide.html#python) for Python source files (if applicable)
 - [ ] I have made corresponding changes to the documentation (if applicable)
 - [ ] I have added tests that prove my fix is effective or that my feature works (if applicable)
diff --git a/.github/workflows/format-check.yml b/.github/workflows/format-check.yml
index 42b28b2cdc6..ddb29be5a4a 100644
--- a/.github/workflows/format-check.yml
+++ b/.github/workflows/format-check.yml
@@ -31,7 +31,7 @@ jobs:
           style: file
           files-changed-only: true
           tidy-checks: '-*'
-          version: '15' # clang-format version
+          version: '18' # clang-format version
           format-review: ${{ github.event_name == 'pull_request' && contains(github.event.pull_request.labels.*.name, 'cpp-format-suggest') }}
           passive-reviews: ${{ github.event_name == 'pull_request' && contains(github.event.pull_request.labels.*.name, 'cpp-format-suggest') }}
           file-annotations: true
diff --git a/AGENTS.md b/AGENTS.md
index d24eb68da67..0ff2abbdc42 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -229,7 +229,7 @@ When modifying C++ public APIs, update corresponding ctypes signatures in `openm
 - **Include order**: Related header first, then C/C++ stdlib, third-party libs, local headers
 - **Comments**: C++-style (`//`) only, never C-style (`/* */`)
 - **Standard**: C++17 features allowed
-- **Formatting**: Run `clang-format` (version 15) before committing; install via `tools/dev/install-commit-hooks.sh`
+- **Formatting**: Run `clang-format` (version 18) before committing; install via `tools/dev/install-commit-hooks.sh`
 
 ### Python Style
 - **PEP8** compliant
@@ -295,4 +295,4 @@ Check for optional features:
 2. **ID conflicts**: Python objects with duplicate IDs trigger `IDWarning`, use `reset_auto_ids()` between tests
 3. **MPI builds**: Code must work with and without MPI; use `#ifdef OPENMC_MPI` guards
 4. **Path handling**: Use `pathlib.Path` in new Python code, not `os.path`
-5. **Clang-format version**: CI uses version 15; other versions may produce different formatting
+5. **Clang-format version**: CI uses version 18; other versions may produce different formatting
diff --git a/docs/source/devguide/styleguide.rst b/docs/source/devguide/styleguide.rst
index 2c882b0341f..a5599566e21 100644
--- a/docs/source/devguide/styleguide.rst
+++ b/docs/source/devguide/styleguide.rst
@@ -30,7 +30,7 @@ whenever a file is saved. For example, `Visual Studio Code
 support for running clang-format.
 
 .. note::
-    OpenMC's CI uses `clang-format` version 15. A different version of `clang-format`
+    OpenMC's CI uses `clang-format` version 18. A different version of `clang-format`
     may produce different line changes and as a result fail the CI test.
 
 Miscellaneous
diff --git a/include/openmc/volume_calc.h b/include/openmc/volume_calc.h
index 9d3f1d02615..ef75ec0653c 100644
--- a/include/openmc/volume_calc.h
+++ b/include/openmc/volume_calc.h
@@ -34,7 +34,7 @@ class VolumeCalculation {
     vector<double> atoms;       //!< Number of atoms for each nuclide
     vector<double> uncertainty; //!< Uncertainty on number of atoms
     int iterations; //!< Number of iterations needed to obtain the results
-  };                // Results for a single domain
+  }; // Results for a single domain
 
   // Constructors
   VolumeCalculation(pugi::xml_node node);
diff --git a/src/mgxs.cpp b/src/mgxs.cpp
index 65a7a0c55ca..a0fe4060ddb 100644
--- a/src/mgxs.cpp
+++ b/src/mgxs.cpp
@@ -365,7 +365,7 @@ Mgxs::Mgxs(const std::string& in_name, const vector<double>& mat_kTs,
           }
         }
       } // end switch
-    }   // end microscopic temperature loop
+    } // end microscopic temperature loop
 
     // Now combine the microscopic data at each relevant temperature
     // We will do this by treating the multiple temperatures of a nuclide as