diff --git a/crates/algokit_transact/src/constants.rs b/crates/algokit_transact/src/constants.rs
index 8ee12feb..f3fa7413 100644
--- a/crates/algokit_transact/src/constants.rs
+++ b/crates/algokit_transact/src/constants.rs
@@ -2,4 +2,5 @@ pub const HASH_BYTES_LENGTH: usize = 32;
 pub const ALGORAND_CHECKSUM_BYTE_LENGTH: usize = 4;
 pub const ALGORAND_ADDRESS_LENGTH: usize = 58;
 pub const ALGORAND_PUBLIC_KEY_BYTE_LENGTH: usize = 32;
+pub const ALGORAND_SIGNATURE_ENCODING_INCR: usize = 75;
 pub type Byte32 = [u8; 32];
diff --git a/crates/algokit_transact/src/lib.rs b/crates/algokit_transact/src/lib.rs
index ca137909..51007df4 100644
--- a/crates/algokit_transact/src/lib.rs
+++ b/crates/algokit_transact/src/lib.rs
@@ -12,7 +12,7 @@ pub use constants::{
     ALGORAND_PUBLIC_KEY_BYTE_LENGTH, HASH_BYTES_LENGTH,
 };
 pub use error::AlgoKitTransactError;
-pub use traits::{AlgorandMsgpack, TransactionId};
+pub use traits::{AlgorandMsgpack, EstimateTransactionSize, TransactionId};
 pub use transactions::{
     AssetTransferTransactionBuilder, AssetTransferTransactionFields, PaymentTransactionBuilder,
     PaymentTransactionFields, SignedTransaction, Transaction, TransactionHeader,
diff --git a/crates/algokit_transact/src/test_utils/mod.rs b/crates/algokit_transact/src/test_utils/mod.rs
index cb7f7101..d0ee164e 100644
--- a/crates/algokit_transact/src/test_utils/mod.rs
+++ b/crates/algokit_transact/src/test_utils/mod.rs
@@ -1,4 +1,3 @@
-use std::fs::File;
 use crate::{
     transactions::{AssetTransferTransactionBuilder, PaymentTransactionBuilder},
     Address, AlgorandMsgpack, Byte32, SignedTransaction, Transaction, TransactionHeaderBuilder,
@@ -9,6 +8,7 @@ use convert_case::{Case, Casing};
 use ed25519_dalek::{Signer, SigningKey};
 use serde::Serialize;
 use serde_json::to_writer_pretty;
+use std::fs::File;
 
 pub struct TransactionHeaderMother {}
 impl TransactionHeaderMother {
@@ -56,8 +56,9 @@ impl TransactionMother {
             .header(TransactionHeaderMother::simple_testnet().build().unwrap())
             .amount(101000)
             .receiver(
-                "VXH5UP6JLU2CGIYPUFZ4Z5OTLJCLMA5EXD3YHTMVNDE5P7ILZ324FSYSPQ".parse::<Address>()
-                    .unwrap()
+                "VXH5UP6JLU2CGIYPUFZ4Z5OTLJCLMA5EXD3YHTMVNDE5P7ILZ324FSYSPQ"
+                    .parse::<Address>()
+                    .unwrap(),
             )
             .to_owned()
     }
@@ -83,8 +84,9 @@ impl TransactionMother {
             .header(
                 TransactionHeaderMother::simple_testnet()
                     .sender(
-                        "JB3K6HTAXODO4THESLNYTSG6GQUFNEVIQG7A6ZYVDACR6WA3ZF52TKU5NA".parse::<Address>()
-                            .unwrap()
+                        "JB3K6HTAXODO4THESLNYTSG6GQUFNEVIQG7A6ZYVDACR6WA3ZF52TKU5NA"
+                            .parse::<Address>()
+                            .unwrap(),
                     )
                     .first_valid(51183672)
                     .last_valid(51183872)
@@ -94,8 +96,9 @@ impl TransactionMother {
             .asset_id(107686045)
             .amount(0)
             .receiver(
-                "JB3K6HTAXODO4THESLNYTSG6GQUFNEVIQG7A6ZYVDACR6WA3ZF52TKU5NA".parse::<Address>()
-                    .unwrap()
+                "JB3K6HTAXODO4THESLNYTSG6GQUFNEVIQG7A6ZYVDACR6WA3ZF52TKU5NA"
+                    .parse::<Address>()
+                    .unwrap(),
             )
             .to_owned()
     }
@@ -108,7 +111,8 @@ impl AddressMother {
     }
 
     pub fn address() -> Address {
-        "RIMARGKZU46OZ77OLPDHHPUJ7YBSHRTCYMQUC64KZCCMESQAFQMYU6SL2Q".parse::<Address>()
+        "RIMARGKZU46OZ77OLPDHHPUJ7YBSHRTCYMQUC64KZCCMESQAFQMYU6SL2Q"
+            .parse::<Address>()
             .unwrap()
     }
 }
diff --git a/crates/algokit_transact/src/traits.rs b/crates/algokit_transact/src/traits.rs
index 03effb5e..b1147787 100644
--- a/crates/algokit_transact/src/traits.rs
+++ b/crates/algokit_transact/src/traits.rs
@@ -58,7 +58,7 @@ pub trait AlgorandMsgpack: Serialize + for<'de> Deserialize<'de> {
     /// * `bytes` - The MessagePack encoded bytes
     ///
     /// # Returns
-    /// The decoded instance or an AlgoKitTransactError if the input is empty or 
+    /// The decoded instance or an AlgoKitTransactError if the input is empty or
     /// deserialization fails.
     fn decode(bytes: &[u8]) -> Result<Self, AlgoKitTransactError> {
         if bytes.is_empty() {
@@ -84,7 +84,7 @@ pub trait AlgorandMsgpack: Serialize + for<'de> Deserialize<'de> {
     ///
     /// This method performs canonical encoding and prepends the domain separation
     /// prefix defined by the PREFIX constant.
-    /// 
+    ///
     /// Use `encode_raw()` if you want to encode without the prefix.
     ///
     /// # Returns
@@ -140,3 +140,7 @@ pub trait TransactionId: AlgorandMsgpack {
         ))
     }
 }
+
+pub trait EstimateTransactionSize: AlgorandMsgpack {
+    fn estimate_size(&self) -> Result<usize, AlgoKitTransactError>;
+}
diff --git a/crates/algokit_transact/src/transactions/mod.rs b/crates/algokit_transact/src/transactions/mod.rs
index 14012ac4..4c8caee0 100644
--- a/crates/algokit_transact/src/transactions/mod.rs
+++ b/crates/algokit_transact/src/transactions/mod.rs
@@ -14,9 +14,9 @@ pub use common::{TransactionHeader, TransactionHeaderBuilder};
 use payment::PaymentTransactionBuilderError;
 pub use payment::{PaymentTransactionBuilder, PaymentTransactionFields};
 
-use crate::constants::HASH_BYTES_LENGTH;
+use crate::constants::{ALGORAND_SIGNATURE_ENCODING_INCR, HASH_BYTES_LENGTH};
 use crate::error::AlgoKitTransactError;
-use crate::traits::{AlgorandMsgpack, TransactionId};
+use crate::traits::{AlgorandMsgpack, EstimateTransactionSize, TransactionId};
 use serde::{Deserialize, Serialize};
 use serde_with::{serde_as, Bytes};
 use std::any::Any;
@@ -59,6 +59,12 @@ impl AssetTransferTransactionBuilder {
 impl AlgorandMsgpack for Transaction {}
 impl TransactionId for Transaction {}
 
+impl EstimateTransactionSize for Transaction {
+    fn estimate_size(&self) -> Result<usize, AlgoKitTransactError> {
+        return Ok(self.encode()?.len() + ALGORAND_SIGNATURE_ENCODING_INCR);
+    }
+}
+
 /// A signed transaction.
 #[serde_as]
 #[derive(Serialize, Deserialize, Debug, PartialEq, Clone)]
@@ -127,3 +133,9 @@ impl TransactionId for SignedTransaction {
         self.transaction.raw_id()
     }
 }
+
+impl EstimateTransactionSize for SignedTransaction {
+    fn estimate_size(&self) -> Result<usize, AlgoKitTransactError> {
+        return Ok(self.encode()?.len());
+    }
+}
diff --git a/crates/algokit_transact_ffi/src/lib.rs b/crates/algokit_transact_ffi/src/lib.rs
index 6eb3cbbe..f882d5f2 100644
--- a/crates/algokit_transact_ffi/src/lib.rs
+++ b/crates/algokit_transact_ffi/src/lib.rs
@@ -1,4 +1,4 @@
-use algokit_transact::{AlgorandMsgpack, Byte32, TransactionId};
+use algokit_transact::{AlgorandMsgpack, Byte32, EstimateTransactionSize, TransactionId};
 use ffi_macros::{ffi_func, ffi_record};
 use serde::{Deserialize, Serialize};
 use serde_bytes::ByteBuf;
@@ -406,6 +406,25 @@ pub fn attach_signature(
     Ok(signed_tx.encode()?)
 }
 
+#[ffi_func]
+/// Return the size of the transaction in bytes as if it was already signed and encoded.
+/// This is useful for estimating the fee for the transaction.
+pub fn estimate_transaction_size(transaction: &Transaction) -> Result<u64, AlgoKitTransactError> {
+    let core_tx: algokit_transact::Transaction = transaction.clone().try_into()?;
+    return core_tx
+        .estimate_size()
+        .map_err(|e| {
+            AlgoKitTransactError::EncodingError(format!(
+                "Failed to estimate transaction size: {}",
+                e
+            ))
+        })?
+        .try_into()
+        .map_err(|_| {
+            AlgoKitTransactError::EncodingError("Failed to convert size to u64".to_string())
+        });
+}
+
 #[ffi_func]
 pub fn address_from_pub_key(pub_key: &[u8]) -> Result<Address, AlgoKitTransactError> {
     Ok(
@@ -418,7 +437,8 @@ pub fn address_from_pub_key(pub_key: &[u8]) -> Result<Address, AlgoKitTransactEr
 
 #[ffi_func]
 pub fn address_from_string(address: &str) -> Result<Address, AlgoKitTransactError> {
-    address.parse::<algokit_transact::Address>()
+    address
+        .parse::<algokit_transact::Address>()
         .map(Into::into)
         .map_err(|e| AlgoKitTransactError::EncodingError(e.to_string()))
 }