diff --git a/src/cargo/core/compiler/timings/mod.rs b/src/cargo/core/compiler/timings/mod.rs
index ce5fbccaa8e..0c0fce23edc 100644
--- a/src/cargo/core/compiler/timings/mod.rs
+++ b/src/cargo/core/compiler/timings/mod.rs
@@ -437,12 +437,14 @@ impl<'gctx> Timings<'gctx> {
                 .iter()
                 .map(|kind| build_runner.bcx.target_data.short_name(kind))
                 .collect::<Vec<_>>();
+            let num_cpus = std::thread::available_parallelism()
+                .ok()
+                .map(|x| x.get() as u64);
 
             let unit_data = report::to_unit_data(&self.unit_times, &self.unit_to_index);
             let concurrency = report::compute_concurrency(&unit_data);
 
             let ctx = report::RenderContext {
-                start: self.start,
                 start_str: &self.start_str,
                 root_units: &self.root_targets,
                 profile: &self.profile,
@@ -455,6 +457,7 @@ impl<'gctx> Timings<'gctx> {
                 host: &build_runner.bcx.rustc().host,
                 requested_targets,
                 jobs: build_runner.bcx.jobs(),
+                num_cpus,
                 error,
             };
             report::write_html(ctx, &mut f)?;
diff --git a/src/cargo/core/compiler/timings/report.rs b/src/cargo/core/compiler/timings/report.rs
index f7b7a7ab3f2..72e76c0fb5d 100644
--- a/src/cargo/core/compiler/timings/report.rs
+++ b/src/cargo/core/compiler/timings/report.rs
@@ -4,7 +4,6 @@ use std::borrow::Cow;
 use std::collections::HashMap;
 use std::collections::HashSet;
 use std::io::Write;
-use std::time::Instant;
 
 use itertools::Itertools as _;
 
@@ -96,8 +95,6 @@ pub struct Concurrency {
 }
 
 pub struct RenderContext<'a> {
-    /// When Cargo started.
-    pub start: Instant,
     /// A rendered string of when compilation started.
     pub start_str: &'a str,
     /// A summary of the root units.
@@ -127,13 +124,16 @@ pub struct RenderContext<'a> {
     pub requested_targets: &'a [&'a str],
     /// The number of jobs specified for this build.
     pub jobs: u32,
+    /// Available parallelism of the compilation environment.
+    pub num_cpus: Option<u64>,
     /// Fatal error during the build.
     pub error: &'a Option<anyhow::Error>,
 }
 
 /// Writes an HTML report.
 pub(super) fn write_html(ctx: RenderContext<'_>, f: &mut impl Write) -> CargoResult<()> {
-    let duration = ctx.start.elapsed().as_secs_f64();
+    // The last concurrency record should equal to the last unit finished time.
+    let duration = ctx.concurrency.last().map(|c| c.t).unwrap_or(0.0);
     let roots: Vec<&str> = ctx
         .root_units
         .iter()
@@ -186,10 +186,11 @@ fn write_summary_table(
     };
     let total_time = format!("{:.1}s{}", duration, time_human);
 
-    let max_concurrency = ctx.concurrency.iter().map(|c| c.active).max().unwrap();
-    let num_cpus = std::thread::available_parallelism()
-        .map(|x| x.get().to_string())
-        .unwrap_or_else(|_| "n/a".into());
+    let max_concurrency = ctx.concurrency.iter().map(|c| c.active).max().unwrap_or(0);
+    let num_cpus = ctx
+        .num_cpus
+        .map(|x| x.to_string())
+        .unwrap_or_else(|| "n/a".into());
 
     let requested_targets = ctx.requested_targets.join(", ");
 
diff --git a/src/cargo/ops/cargo_compile/mod.rs b/src/cargo/ops/cargo_compile/mod.rs
index cc90bddea93..92c80129031 100644
--- a/src/cargo/ops/cargo_compile/mod.rs
+++ b/src/cargo/ops/cargo_compile/mod.rs
@@ -162,10 +162,14 @@ pub fn compile_ws<'a>(
 
     if let Some(ref logger) = logger {
         let rustc = ws.gctx().load_global_rustc(Some(ws))?;
+        let num_cpus = std::thread::available_parallelism()
+            .ok()
+            .map(|x| x.get() as u64);
         logger.log(LogMessage::BuildStarted {
             cwd: ws.gctx().cwd().to_path_buf(),
             host: rustc.host.to_string(),
             jobs: options.build_config.jobs,
+            num_cpus,
             profile: options.build_config.requested_profile.to_string(),
             rustc_version: rustc.version.to_string(),
             rustc_version_verbose: rustc.verbose_version.clone(),
diff --git a/src/cargo/util/log_message.rs b/src/cargo/util/log_message.rs
index e0cf19f7769..9ab10d6bdb0 100644
--- a/src/cargo/util/log_message.rs
+++ b/src/cargo/util/log_message.rs
@@ -24,6 +24,8 @@ pub enum LogMessage {
         host: String,
         /// Number of parallel jobs.
         jobs: u32,
+        /// Available parallelism of the compilation environment.
+        num_cpus: Option<u64>,
         /// Build profile name (e.g., "dev", "release").
         profile: String,
         /// The rustc version (`1.23.4-beta.2`).
diff --git a/tests/testsuite/build_analysis.rs b/tests/testsuite/build_analysis.rs
index 4a15bed21a5..b8528052d61 100644
--- a/tests/testsuite/build_analysis.rs
+++ b/tests/testsuite/build_analysis.rs
@@ -80,6 +80,7 @@ fn log_msg_build_started() {
     "cwd": "[ROOT]/foo",
     "host": "[HOST_TARGET]",
     "jobs": "{...}",
+    "num_cpus": "{...}",
     "profile": "dev",
     "reason": "build-started",
     "run_id": "[..]T[..]Z-[..]",