diff --git a/internal/middleware/logging.go b/internal/middleware/logging.go
index 7bc34e2..cda6f7c 100644
--- a/internal/middleware/logging.go
+++ b/internal/middleware/logging.go
@@ -3,12 +3,38 @@ package middleware
 import (
 	"log/slog"
 	"net/http"
+	"time"
 )
 
+// Clock abstracts the time source so the middleware can be tested
+// deterministically.
+type Clock interface {
+	Now() time.Time
+	Since(t time.Time) time.Duration
+}
+
+type systemClock struct{}
+
+func (systemClock) Now() time.Time                  { return time.Now() }
+func (systemClock) Since(t time.Time) time.Duration { return time.Since(t) }
+
+// DefaultClock is the wall clock used by Logging.
+var DefaultClock Clock = systemClock{}
+
 // Logging writes one structured line per request after it completes.
 func Logging(logger *slog.Logger, next http.Handler) http.Handler {
+	return LoggingWithClock(logger, DefaultClock, next)
+}
+
+// LoggingWithClock is Logging with an injectable time source.
+func LoggingWithClock(logger *slog.Logger, clock Clock, next http.Handler) http.Handler {
 	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		start := clock.Now()
 		next.ServeHTTP(w, r)
-		logger.Info("request", "method", r.Method, "path", r.URL.Path)
+		logger.Info("request",
+			"method", r.Method,
+			"path", r.URL.Path,
+			"duration_ms", clock.Since(start).Milliseconds(),
+		)
 	})
 }