From 896080050a4fe7e347e0b0779bb729f6bbd9d068 Mon Sep 17 00:00:00 2001
From: Marco Granelli <marco@heliax.dev>
Date: Fri, 12 Dec 2025 12:01:27 +0100
Subject: [PATCH 1/3] Makes `compute_masp_frontend_sus_fee` public

---
 crates/sdk/src/tx.rs | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/crates/sdk/src/tx.rs b/crates/sdk/src/tx.rs
index 93f643562d..c6d57aec27 100644
--- a/crates/sdk/src/tx.rs
+++ b/crates/sdk/src/tx.rs
@@ -3616,8 +3616,8 @@ async fn get_masp_fee_payment_amount<N: Namada>(
     })
 }
 
-// Extract the validate amount for the masp frontend sustainability fee
-async fn compute_masp_frontend_sus_fee(
+/// Extract the validate amount for the masp frontend sustainability fee
+pub async fn compute_masp_frontend_sus_fee(
     context: &impl Namada,
     input_amount: &namada_token::DenominatedAmount,
     percentage: &namada_core::dec::Dec,

From b6bf629d07db603b1aa8d3e521f095c4010cce50 Mon Sep 17 00:00:00 2001
From: Marco Granelli <marco@heliax.dev>
Date: Fri, 12 Dec 2025 12:05:36 +0100
Subject: [PATCH 2/3] Changelog #5001

---
 .changelog/unreleased/SDK/5001-pub-frontendfee-builder.md | 3 +++
 1 file changed, 3 insertions(+)
 create mode 100644 .changelog/unreleased/SDK/5001-pub-frontendfee-builder.md

diff --git a/.changelog/unreleased/SDK/5001-pub-frontendfee-builder.md b/.changelog/unreleased/SDK/5001-pub-frontendfee-builder.md
new file mode 100644
index 0000000000..e034223698
--- /dev/null
+++ b/.changelog/unreleased/SDK/5001-pub-frontendfee-builder.md
@@ -0,0 +1,3 @@
+- The SDK now exposes the function to derive the validated amount of the
+  MASP frontend sustainability fee. ([\#5001](https://github.com/namada-
+  net/namada/pull/5001))
\ No newline at end of file

From db30c308bd5d71e28b41804fcf6016be7ae1769e Mon Sep 17 00:00:00 2001
From: Marco Granelli <marco@heliax.dev>
Date: Thu, 18 Dec 2025 15:02:35 +0100
Subject: [PATCH 3/3] Rounds up the frontend fee

---
 crates/sdk/src/tx.rs | 33 +++++++++++++++++----------------
 1 file changed, 17 insertions(+), 16 deletions(-)

diff --git a/crates/sdk/src/tx.rs b/crates/sdk/src/tx.rs
index c6d57aec27..374b26df45 100644
--- a/crates/sdk/src/tx.rs
+++ b/crates/sdk/src/tx.rs
@@ -3624,23 +3624,24 @@ pub async fn compute_masp_frontend_sus_fee(
     token: &Address,
     force: bool,
 ) -> Result<namada_token::DenominatedAmount> {
-    let sus_fee_amt = namada_token::Amount::from_uint(
-        input_amount
-            .amount()
-            .raw_amount()
-            .checked_mul_div(
-                percentage.abs(),
-                namada_core::uint::Uint::exp10(POS_DECIMAL_PRECISION as _),
+    let (mut amount, remainder) = input_amount
+        .amount()
+        .raw_amount()
+        .checked_mul_div(
+            percentage.abs(),
+            namada_core::uint::Uint::exp10(POS_DECIMAL_PRECISION as _),
+        )
+        .ok_or_else(|| {
+            Error::Other(
+                "Overflow in masp frontend fee computation".to_string(),
             )
-            .ok_or_else(|| {
-                Error::Other(
-                    "Overflow in masp frontend fee computation".to_string(),
-                )
-            })?
-            .0,
-        0,
-    )
-    .map_err(|e| Error::Other(e.to_string()))?;
+        })?;
+    if !remainder.is_zero() {
+        // Round up the fee
+        amount += 1.into();
+    }
+    let sus_fee_amt = namada_token::Amount::from_uint(amount, 0)
+        .map_err(|e| Error::Other(e.to_string()))?;
 
     // Validate the amount given
     validate_amount(