diff --git a/central_backend/src/energy/relay_state_history.rs b/central_backend/src/energy/relay_state_history.rs
index ac22b1a..0eafaf4 100644
--- a/central_backend/src/energy/relay_state_history.rs
+++ b/central_backend/src/energy/relay_state_history.rs
@@ -64,6 +64,11 @@ impl RelayStateHistory {
         Ok(((relative_time / 8) as usize, (relative_time % 8) as u8))
     }
 
+    /// Check if a time is contained in this history
+    pub fn contains_time(&self, time: u64) -> bool {
+        self.resolve_offset(time).is_ok()
+    }
+
     /// Set new state of relay
     pub fn set_state(&mut self, time: u64, on: bool) -> anyhow::Result<()> {
         let (idx, offset) = self.resolve_offset(time)?;
@@ -93,10 +98,31 @@ impl RelayStateHistory {
     }
 }
 
+/// Get the total runtime of a relay during a given time window
+pub fn relay_total_runtime(device_id: DeviceRelayID, from: u64, to: u64) -> anyhow::Result<usize> {
+    let mut total = 0;
+    let mut file = RelayStateHistory::open(device_id, from)?;
+    let mut curr_time = from;
+
+    while curr_time < to {
+        if !file.contains_time(curr_time) {
+            file = RelayStateHistory::open(device_id, curr_time)?;
+        }
+
+        if file.get_state(curr_time)? {
+            total += TIME_INTERVAL;
+        }
+
+        curr_time += TIME_INTERVAL as u64;
+    }
+
+    Ok(total)
+}
+
 #[cfg(test)]
 mod tests {
     use crate::devices::device::DeviceRelayID;
-    use crate::energy::relay_state_history::RelayStateHistory;
+    use crate::energy::relay_state_history::{relay_total_runtime, RelayStateHistory};
 
     #[test]
     fn test_relay_state_history() {
@@ -138,4 +164,12 @@ mod tests {
 
         assert!(history.get_state(8989898).is_err());
     }
+
+    #[test]
+    fn test_relay_total_runtime() {
+        assert_eq!(
+            relay_total_runtime(DeviceRelayID::default(), 50, 3600 * 24 * 60 + 500).unwrap(),
+            0
+        );
+    }
 }