diff --git a/src/main/java/me/braydon/license/exception/LicenseExpiredException.java b/src/main/java/me/braydon/license/exception/LicenseExpiredException.java
new file mode 100644
index 0000000..03268bd
--- /dev/null
+++ b/src/main/java/me/braydon/license/exception/LicenseExpiredException.java
@@ -0,0 +1,17 @@
+package me.braydon.license.exception;
+
+import me.braydon.license.model.License;
+import org.springframework.http.HttpStatus;
+
+/**
+ * This exception is raised when
+ * a {@link License} has been used
+ * but is expired.
+ *
+ * @author Braydon
+ */
+public class LicenseExpiredException extends APIException {
+    public LicenseExpiredException() {
+        super(HttpStatus.BAD_REQUEST, "License has expired");
+    }
+}
diff --git a/src/main/java/me/braydon/license/model/License.java b/src/main/java/me/braydon/license/model/License.java
index b29aaca..c642c91 100644
--- a/src/main/java/me/braydon/license/model/License.java
+++ b/src/main/java/me/braydon/license/model/License.java
@@ -64,6 +64,14 @@ public class License {
      */
     private int hwidLimit;
     
+    /**
+     * The duration that this licensee is valid for.
+     * <p>
+     * If -1, the license will be permanent.
+     * </p>
+     */
+    private long duration;
+    
     /**
      * The {@link Date} this license was last used.
      */
@@ -74,6 +82,34 @@ public class License {
      */
     @NonNull private Date created;
     
+    /**
+     * Check if this license has expired.
+     * <p>
+     * If this license has no
+     * expiration, this will
+     * always return false.
+     * </p>
+     *
+     * @return true if expired, otherwise false
+     */
+    public boolean hasExpired() {
+        // License is permanent, not expired
+        if (isPermanent()) {
+            return false;
+        }
+        // Check if the license has expired
+        return System.currentTimeMillis() - created.getTime() >= duration;
+    }
+    
+    /**
+     * Check if this license has no expiration.
+     *
+     * @return true if permanent, otherwise false
+     */
+    public boolean isPermanent() {
+        return duration == -1L;
+    }
+    
     /**
      * Invoked when this license is used.
      *
diff --git a/src/main/java/me/braydon/license/service/LicenseService.java b/src/main/java/me/braydon/license/service/LicenseService.java
index 90da960..ed4c172 100644
--- a/src/main/java/me/braydon/license/service/LicenseService.java
+++ b/src/main/java/me/braydon/license/service/LicenseService.java
@@ -4,6 +4,7 @@ import jakarta.annotation.PostConstruct;
 import lombok.NonNull;
 import lombok.extern.slf4j.Slf4j;
 import me.braydon.license.exception.APIException;
+import me.braydon.license.exception.LicenseExpiredException;
 import me.braydon.license.exception.LicenseNotFoundException;
 import me.braydon.license.model.License;
 import me.braydon.license.repository.LicenseRepository;
@@ -66,11 +67,12 @@ public final class LicenseService {
      * @param description the optional description of the license
      * @param ipLimit     the IP limit of the license
      * @param hwidLimit   the HWID limit of the license
+     * @param duration    the duration of the license, -1 for permanent
      * @return the created license
      * @see License for license
      */
-    public License create(@NonNull String key, @NonNull String product,
-                          String description, int ipLimit, int hwidLimit) {
+    public License create(@NonNull String key, @NonNull String product, String description,
+                          int ipLimit, int hwidLimit, long duration) {
         // Create the new license
         License license = new License();
         license.setKey(BCrypt.hashpw(key, licensesSalt)); // Hash the key
@@ -80,6 +82,7 @@ public final class LicenseService {
         license.setHwids(new HashSet<>());
         license.setIpLimit(ipLimit); // Use the given IP limit
         license.setHwidLimit(hwidLimit); // Use the given HWID limit
+        license.setDuration(duration);
         license.setCreated(new Date());
         repository.insert(license); // Insert the newly created license
         return license;
@@ -103,6 +106,9 @@ public final class LicenseService {
             throw new LicenseNotFoundException();
         }
         License license = optionalLicense.get(); // The license found
+        if (license.hasExpired()) { // The license has expired
+            throw new LicenseExpiredException();
+        }
         license.use(ip, ipsSalt, hwid); // Use the license
         repository.save(license); // Save the used license
         log.info("License key {} for product {} was used by {} ({})", key, product, ip, hwid);