diff --git a/backon/src/backoff/constant.rs b/backon/src/backoff/constant.rs
index 277abd6..486ca34 100644
--- a/backon/src/backoff/constant.rs
+++ b/backon/src/backoff/constant.rs
@@ -41,6 +41,13 @@ pub struct ConstantBuilder {
 
 impl Default for ConstantBuilder {
     fn default() -> Self {
+        Self::new()
+    }
+}
+
+impl ConstantBuilder {
+    /// Create a new `ConstantBuilder` with default values.
+    pub const fn new() -> Self {
         Self {
             delay: Duration::from_secs(1),
             max_times: Some(3),
@@ -48,17 +55,15 @@ impl Default for ConstantBuilder {
             seed: None,
         }
     }
-}
 
-impl ConstantBuilder {
     /// Set the delay for the backoff.
-    pub fn with_delay(mut self, delay: Duration) -> Self {
+    pub const fn with_delay(mut self, delay: Duration) -> Self {
         self.delay = delay;
         self
     }
 
     /// Set the maximum number of attempts to be made.
-    pub fn with_max_times(mut self, max_times: usize) -> Self {
+    pub const fn with_max_times(mut self, max_times: usize) -> Self {
         self.max_times = Some(max_times);
         self
     }
@@ -66,7 +71,7 @@ impl ConstantBuilder {
     /// Enable jitter for the backoff.
     ///
     /// Jitter is a random value added to the delay to prevent a thundering herd problem.
-    pub fn with_jitter(mut self) -> Self {
+    pub const fn with_jitter(mut self) -> Self {
         self.jitter = true;
         self
     }
@@ -82,7 +87,7 @@ impl ConstantBuilder {
     /// The backoff will not stop by itself.
     ///
     /// _The backoff could stop reaching `usize::MAX` attempts but this is **unrealistic**._
-    pub fn without_max_times(mut self) -> Self {
+    pub const fn without_max_times(mut self) -> Self {
         self.max_times = None;
         self
     }
@@ -159,13 +164,16 @@ impl Iterator for ConstantBackoff {
 
 #[cfg(test)]
 mod tests {
+    use super::*;
     use core::time::Duration;
 
     #[cfg(target_arch = "wasm32")]
     use wasm_bindgen_test::wasm_bindgen_test as test;
 
-    use crate::BackoffBuilder;
-    use crate::ConstantBuilder;
+    const TEST_BUILDER: ConstantBuilder = ConstantBuilder::new()
+        .with_delay(Duration::from_secs(2))
+        .with_max_times(5)
+        .with_jitter();
 
     #[test]
     fn test_constant_default() {
@@ -214,4 +222,13 @@ mod tests {
             assert_eq!(Some(Duration::from_secs(1)), it.next());
         }
     }
+
+    // allow assertions on constants because they are not optimized out by unit tests 
+    #[allow(clippy::assertions_on_constants)]
+    #[test]
+    fn test_constant_const_builder() {
+        assert_eq!(TEST_BUILDER.delay, Duration::from_secs(2));
+        assert_eq!(TEST_BUILDER.max_times, Some(5));
+        assert!(TEST_BUILDER.jitter);
+    }
 }
diff --git a/backon/src/backoff/exponential.rs b/backon/src/backoff/exponential.rs
index 202c314..3bb32c2 100644
--- a/backon/src/backoff/exponential.rs
+++ b/backon/src/backoff/exponential.rs
@@ -46,6 +46,13 @@ pub struct ExponentialBuilder {
 
 impl Default for ExponentialBuilder {
     fn default() -> Self {
+        Self::new()
+    }
+}
+
+impl ExponentialBuilder {
+    /// Create a new `ExponentialBuilder` with default values.
+    pub const fn new() -> Self {
         Self {
             jitter: false,
             factor: 2.0,
@@ -55,14 +62,12 @@ impl Default for ExponentialBuilder {
             seed: None,
         }
     }
-}
 
-impl ExponentialBuilder {
     /// Enable jitter for the backoff.
     ///
     /// When jitter is enabled, [`ExponentialBackoff`] will add a random jitter within `(0, min_delay)`
     /// to the current delay.
-    pub fn with_jitter(mut self) -> Self {
+    pub const fn with_jitter(mut self) -> Self {
         self.jitter = true;
         self
     }
@@ -78,7 +83,7 @@ impl ExponentialBuilder {
     /// # Panics
     ///
     /// This function will panic if the input factor is less than `1.0`.
-    pub fn with_factor(mut self, factor: f32) -> Self {
+    pub const fn with_factor(mut self, factor: f32) -> Self {
         debug_assert!(factor >= 1.0, "invalid factor that lower than 1");
 
         self.factor = factor;
@@ -86,7 +91,7 @@ impl ExponentialBuilder {
     }
 
     /// Set the minimum delay for the backoff.
-    pub fn with_min_delay(mut self, min_delay: Duration) -> Self {
+    pub const fn with_min_delay(mut self, min_delay: Duration) -> Self {
         self.min_delay = min_delay;
         self
     }
@@ -94,7 +99,7 @@ impl ExponentialBuilder {
     /// Set the maximum delay for the backoff.
     ///
     /// The delay will not increase if the current delay exceeds the maximum delay.
-    pub fn with_max_delay(mut self, max_delay: Duration) -> Self {
+    pub const fn with_max_delay(mut self, max_delay: Duration) -> Self {
         self.max_delay = Some(max_delay);
         self
     }
@@ -104,7 +109,7 @@ impl ExponentialBuilder {
     /// The delay will keep increasing.
     ///
     /// _The delay will saturate at `Duration::MAX` which is an **unrealistic** delay._
-    pub fn without_max_delay(mut self) -> Self {
+    pub const fn without_max_delay(mut self) -> Self {
         self.max_delay = None;
         self
     }
@@ -112,7 +117,7 @@ impl ExponentialBuilder {
     /// Set the maximum number of attempts for the current backoff.
     ///
     /// The backoff will stop if the maximum number of attempts is reached.
-    pub fn with_max_times(mut self, max_times: usize) -> Self {
+    pub const fn with_max_times(mut self, max_times: usize) -> Self {
         self.max_times = Some(max_times);
         self
     }
@@ -122,7 +127,7 @@ impl ExponentialBuilder {
     /// The backoff will not stop by itself.
     ///
     /// _The backoff could stop reaching `usize::MAX` attempts but this is **unrealistic**._
-    pub fn without_max_times(mut self) -> Self {
+    pub const fn without_max_times(mut self) -> Self {
         self.max_times = None;
         self
     }
@@ -235,6 +240,13 @@ mod tests {
     use crate::BackoffBuilder;
     use crate::ExponentialBuilder;
 
+    const TEST_BUILDER: ExponentialBuilder = ExponentialBuilder::new()
+        .with_jitter()
+        .with_factor(1.5)
+        .with_min_delay(Duration::from_secs(2))
+        .with_max_delay(Duration::from_secs(30))
+        .with_max_times(5);
+
     #[test]
     fn test_exponential_default() {
         let mut exp = ExponentialBuilder::default().build();
@@ -389,4 +401,15 @@ mod tests {
         assert_eq!(Some(Duration::from_secs(1)), exp.next());
         assert_eq!(None, exp.next());
     }
+
+    // allow assertions on constants because they are not optimized out by unit tests 
+    #[allow(clippy::assertions_on_constants)]
+    #[test]
+    fn test_exponential_const_builder() {
+        assert!(TEST_BUILDER.jitter);
+        assert_eq!(TEST_BUILDER.factor, 1.5);
+        assert_eq!(TEST_BUILDER.min_delay, Duration::from_secs(2));
+        assert_eq!(TEST_BUILDER.max_delay, Some(Duration::from_secs(30)));
+        assert_eq!(TEST_BUILDER.max_times, Some(5));
+    }
 }
diff --git a/backon/src/backoff/fibonacci.rs b/backon/src/backoff/fibonacci.rs
index 27bf5ae..22d13eb 100644
--- a/backon/src/backoff/fibonacci.rs
+++ b/backon/src/backoff/fibonacci.rs
@@ -44,6 +44,13 @@ pub struct FibonacciBuilder {
 
 impl Default for FibonacciBuilder {
     fn default() -> Self {
+        Self::new()
+    }
+}
+
+impl FibonacciBuilder {
+    /// Create a new `FibonacciBuilder` with default values.
+    pub const fn new() -> Self {
         Self {
             jitter: false,
             seed: None,
@@ -52,13 +59,11 @@ impl Default for FibonacciBuilder {
             max_times: Some(3),
         }
     }
-}
 
-impl FibonacciBuilder {
     /// Set the jitter for the backoff.
     ///
     /// When jitter is enabled, FibonacciBackoff will add a random jitter between `(0, min_delay)` to the delay.
-    pub fn with_jitter(mut self) -> Self {
+    pub const fn with_jitter(mut self) -> Self {
         self.jitter = true;
         self
     }
@@ -70,7 +75,7 @@ impl FibonacciBuilder {
     }
 
     /// Set the minimum delay for the backoff.
-    pub fn with_min_delay(mut self, min_delay: Duration) -> Self {
+    pub const fn with_min_delay(mut self, min_delay: Duration) -> Self {
         self.min_delay = min_delay;
         self
     }
@@ -78,7 +83,7 @@ impl FibonacciBuilder {
     /// Set the maximum delay for the current backoff.
     ///
     /// The delay will not increase if the current delay exceeds the maximum delay.
-    pub fn with_max_delay(mut self, max_delay: Duration) -> Self {
+    pub const fn with_max_delay(mut self, max_delay: Duration) -> Self {
         self.max_delay = Some(max_delay);
         self
     }
@@ -88,7 +93,7 @@ impl FibonacciBuilder {
     /// The delay will keep increasing.
     ///
     /// _The delay will saturate at `Duration::MAX` which is an **unrealistic** delay._
-    pub fn without_max_delay(mut self) -> Self {
+    pub const fn without_max_delay(mut self) -> Self {
         self.max_delay = None;
         self
     }
@@ -96,7 +101,7 @@ impl FibonacciBuilder {
     /// Set the maximum number of attempts for the current backoff.
     ///
     /// The backoff will stop if the maximum number of attempts is reached.
-    pub fn with_max_times(mut self, max_times: usize) -> Self {
+    pub const fn with_max_times(mut self, max_times: usize) -> Self {
         self.max_times = Some(max_times);
         self
     }
@@ -106,7 +111,7 @@ impl FibonacciBuilder {
     /// The backoff will not stop by itself.
     ///
     /// _The backoff could stop reaching `usize::MAX` attempts but this is **unrealistic**._
-    pub fn without_max_times(mut self) -> Self {
+    pub const fn without_max_times(mut self) -> Self {
         self.max_times = None;
         self
     }
@@ -212,13 +217,17 @@ impl Iterator for FibonacciBackoff {
 
 #[cfg(test)]
 mod tests {
+    use super::*;
     use core::time::Duration;
 
     #[cfg(target_arch = "wasm32")]
     use wasm_bindgen_test::wasm_bindgen_test as test;
 
-    use crate::BackoffBuilder;
-    use crate::FibonacciBuilder;
+    const TEST_BUILDER: FibonacciBuilder = FibonacciBuilder::new()
+        .with_jitter()
+        .with_min_delay(Duration::from_secs(2))
+        .with_max_delay(Duration::from_secs(30))
+        .with_max_times(5);
 
     #[test]
     fn test_fibonacci_default() {
@@ -322,4 +331,14 @@ mod tests {
             assert_eq!(Some(Duration::from_secs(0)), fib.next());
         }
     }
+
+    // allow assertions on constants because they are not optimized out by unit tests 
+    #[allow(clippy::assertions_on_constants)]
+    #[test]
+    fn test_fibonacci_const_builder() {
+        assert!(TEST_BUILDER.jitter);
+        assert_eq!(TEST_BUILDER.min_delay, Duration::from_secs(2));
+        assert_eq!(TEST_BUILDER.max_delay, Some(Duration::from_secs(30)));
+        assert_eq!(TEST_BUILDER.max_times, Some(5));
+    }
 }