diff --git a/acmed/src/certificate.rs b/acmed/src/certificate.rs
index 739936a..28e245d 100644
--- a/acmed/src/certificate.rs
+++ b/acmed/src/certificate.rs
@@ -70,14 +70,14 @@ impl Certificate {
 		Err(format!("{identifier}: identifier not found").into())
 	}
 
-	fn is_expiring(&self, cert: &X509Certificate) -> Result<bool, Error> {
+	fn renew_in(&self, cert: &X509Certificate) -> Result<Duration, Error> {
 		let expires_in = cert.expires_in()?;
 		self.debug(&format!(
 			"certificate expires in {} days ({} days delay)",
 			expires_in.as_secs() / 86400,
 			self.renew_delay.as_secs() / 86400,
 		));
-		Ok(expires_in <= self.renew_delay)
+		Ok(expires_in.saturating_sub(self.renew_delay))
 	}
 
 	fn has_missing_identifiers(&self, cert: &X509Certificate) -> bool {
@@ -110,33 +110,22 @@ impl Certificate {
 			.join(",")
 	}
 
-	pub async fn should_renew(&self) -> Result<bool, Error> {
+	pub async fn schedule_renewal(&self) -> Result<Duration, Error> {
 		self.debug(&format!(
 			"checking for renewal (identifiers: {})",
 			self.identifier_list()
 		));
 		if !certificate_files_exists(&self.file_manager) {
 			self.debug("certificate does not exist: requesting one");
-			return Ok(true);
+			return Ok(Duration::ZERO);
 		}
 		let cert = get_certificate(&self.file_manager).await?;
 
-		let renew_ident = self.has_missing_identifiers(&cert);
-		if renew_ident {
+		if self.has_missing_identifiers(&cert) {
 			self.debug("the current certificate doesn't include all the required identifiers");
+			return Ok(Duration::ZERO);
 		}
-		let renew_exp = self.is_expiring(&cert)?;
-		if renew_exp {
-			self.debug("the certificate is expiring");
-		}
-		let renew = renew_ident || renew_exp;
-
-		if renew {
-			self.debug("the certificate will be renewed now");
-		} else {
-			self.debug("the certificate will not be renewed now");
-		}
-		Ok(renew)
+		Ok(self.renew_in(&cert)?)
 	}
 
 	pub async fn call_challenge_hooks(
diff --git a/acmed/src/main.rs b/acmed/src/main.rs
index a933867..3cbe93e 100644
--- a/acmed/src/main.rs
+++ b/acmed/src/main.rs
@@ -33,7 +33,6 @@ pub const DEFAULT_CERT_DIR: &str = env!("ACMED_DEFAULT_CERT_DIR");
 pub const DEFAULT_CERT_FORMAT: &str = env!("ACMED_DEFAULT_CERT_FORMAT");
 pub const DEFAULT_CONFIG_FILE: &str = env!("ACMED_DEFAULT_CONFIG_FILE");
 pub const DEFAULT_PID_FILE: &str = env!("ACMED_DEFAULT_PID_FILE");
-pub const DEFAULT_SLEEP_TIME: u64 = 3600;
 pub const DEFAULT_POOL_TIME: u64 = 5000;
 pub const DEFAULT_CSR_DIGEST: HashFunction = HashFunction::Sha256;
 pub const DEFAULT_CERT_KEY_TYPE: KeyType = KeyType::Rsa2048;
diff --git a/acmed/src/main_event_loop.rs b/acmed/src/main_event_loop.rs
index 85456c2..c3c2c4d 100644
--- a/acmed/src/main_event_loop.rs
+++ b/acmed/src/main_event_loop.rs
@@ -179,15 +179,23 @@ async fn renew_certificate(
 	account_s: AccountSync,
 	endpoint_s: EndpointSync,
 ) -> (&mut Certificate, AccountSync, EndpointSync) {
+	let backoff = [60, 10 * 60, 100 * 60, 24 * 60 * 60];
+	let mut scheduling_retries = 0;
 	loop {
-		match certificate.should_renew().await {
-			Ok(true) => break,
-			Ok(false) => {}
+		match certificate.schedule_renewal().await {
+			Ok(duration) => {
+				sleep(duration).await;
+				break;
+			}
 			Err(e) => {
 				certificate.warn(&e.message);
+				sleep(Duration::from_secs(
+					backoff[scheduling_retries.min(backoff.len() - 1)],
+				))
+				.await;
+				scheduling_retries += 1;
 			}
 		}
-		sleep(Duration::from_secs(crate::DEFAULT_SLEEP_TIME)).await;
 	}
 	let (status, is_success) =
 		match request_certificate(certificate, account_s.clone(), endpoint_s.clone()).await {