diff --git a/src/export/markdown.rs b/src/export/markdown.rs
index b6f2425..f677bab 100644
--- a/src/export/markdown.rs
+++ b/src/export/markdown.rs
@@ -80,12 +80,13 @@ pub fn render(report: &Report) -> String {
     lines.join("\n") + "\n"
 }
 
-/// The end time, marked "(+1)" when it falls on the next calendar day.
+/// The end time, marked "(+1)" when it falls on the next calendar day (or
+/// "(-1)" the day before).
 fn out_time(report: &Report, day: &WorkDay, end: Timestamp) -> String {
     let days_later = report.local(end).date().duration_since(day.date()).as_hours() / 24;
     match days_later {
         0 => report.time(end),
-        later => format!("{} (+{later})", report.time(end)),
+        later => format!("{} ({later:+})", report.time(end)),
     }
 }
 
diff --git a/src/ui/component.rs b/src/ui/component.rs
index 82b0940..642bd1a 100644
--- a/src/ui/component.rs
+++ b/src/ui/component.rs
@@ -92,12 +92,14 @@ impl Context<'_> {
         self.fmt.time(self.local(moment).time())
     }
 
-    /// A clock time, marked "+1" when it falls the day after `day`.
+    /// A clock time, marked "+1" when it falls the day after `day` (or "-1"
+    /// the day before, which a backdated start can do).
     pub fn time_on(&self, moment: Timestamp, day: Date) -> String {
         let days_later = self.local(moment).date().duration_since(day).as_hours() / 24;
         match days_later {
             0 => self.time(moment),
-            later => format!("{} +{later}", self.time(moment)),
+            // `:+` always writes the sign: +1, -1.
+            later => format!("{} {later:+}", self.time(moment)),
         }
     }