diff --git a/crates/cli/src/args.rs b/crates/cli/src/args.rs
index c861c25b..cd886739 100644
--- a/crates/cli/src/args.rs
+++ b/crates/cli/src/args.rs
@@ -29,6 +29,8 @@ pub enum TxCommand {
         slot_length: u64,
         #[clap(short, long)]
         zero_time: u64,
+        #[clap(short, long)]
+        zero_slot: u64,
     },
 }
 
diff --git a/crates/cli/src/main.rs b/crates/cli/src/main.rs
index 39e4cc51..23915c87 100644
--- a/crates/cli/src/main.rs
+++ b/crates/cli/src/main.rs
@@ -30,6 +30,7 @@ fn main() -> anyhow::Result<()> {
                 resolved_inputs,
                 slot_length,
                 zero_time,
+                zero_slot,
             } => {
                 let tx_bytes = if cbor {
                     fs::read(input)?
@@ -51,6 +52,7 @@ fn main() -> anyhow::Result<()> {
 
                     let slot_config = SlotConfig {
                         zero_time,
+                        zero_slot,
                         slot_length,
                     };
 
diff --git a/crates/uplc/src/tx.rs b/crates/uplc/src/tx.rs
index 35c8de7e..8996efd0 100644
--- a/crates/uplc/src/tx.rs
+++ b/crates/uplc/src/tx.rs
@@ -68,12 +68,13 @@ pub fn eval_phase_two(
 /// This function is the same as [`eval_phase_two`]
 /// but the inputs are raw bytes.
 /// initial_budget expects (cpu, mem).
+/// slot_config (zero_time, zero_slot, slot_length)
 pub fn eval_phase_two_raw(
     tx_bytes: &[u8],
     utxos_bytes: &[(Vec<u8>, Vec<u8>)],
     cost_mdls_bytes: &[u8],
     initial_budget: (u64, u64),
-    slot_config: (u64, u64),
+    slot_config: (u64, u64, u64),
     run_phase_one: bool,
 ) -> Result<Vec<Vec<u8>>, Error> {
     let multi_era_tx = MultiEraTx::decode(Era::Babbage, tx_bytes)
@@ -97,7 +98,8 @@ pub fn eval_phase_two_raw(
 
     let sc = SlotConfig {
         zero_time: slot_config.0,
-        slot_length: slot_config.1,
+        zero_slot: slot_config.1,
+        slot_length: slot_config.2,
     };
 
     match multi_era_tx {
diff --git a/crates/uplc/src/tx/eval.rs b/crates/uplc/src/tx/eval.rs
index 9d7750bb..19212bd6 100644
--- a/crates/uplc/src/tx/eval.rs
+++ b/crates/uplc/src/tx/eval.rs
@@ -24,7 +24,7 @@ use super::{
 };
 
 fn slot_to_begin_posix_time(slot: u64, sc: &SlotConfig) -> u64 {
-    let ms_after_begin = slot * sc.slot_length;
+    let ms_after_begin = (slot - sc.zero_slot) * sc.slot_length;
     sc.zero_time + ms_after_begin
 }
 
diff --git a/crates/uplc/src/tx/script_context.rs b/crates/uplc/src/tx/script_context.rs
index f762e441..65497dec 100644
--- a/crates/uplc/src/tx/script_context.rs
+++ b/crates/uplc/src/tx/script_context.rs
@@ -84,6 +84,7 @@ pub struct TimeRange {
 
 pub struct SlotConfig {
     pub slot_length: u64,
+    pub zero_slot: u64,
     pub zero_time: u64,
 }
 
@@ -91,7 +92,8 @@ impl Default for SlotConfig {
     fn default() -> Self {
         Self {
             slot_length: 1000,
-            zero_time: 1596491091,
+            zero_slot: 4492800,
+            zero_time: 1596059091000,
         }
     }
 }
diff --git a/crates/uplc/src/tx/tests.rs b/crates/uplc/src/tx/tests.rs
index 9fd84405..d37e1c48 100644
--- a/crates/uplc/src/tx/tests.rs
+++ b/crates/uplc/src/tx/tests.rs
@@ -42,6 +42,7 @@ fn test_eval() {
 
     let slot_config = SlotConfig {
         zero_time: 1660003200000, // Preview network
+        zero_slot: 0,
         slot_length: 1000,
     };
 
@@ -292,6 +293,7 @@ fn test_eval_1() {
 
     let slot_config = SlotConfig {
         zero_time: 1660003200000, // Preview network
+        zero_slot: 0,
         slot_length: 1000,
     };
 
@@ -561,6 +563,7 @@ fn test_eval_2() {
 
     let slot_config = SlotConfig {
         zero_time: 1660003200000, // Preview network
+        zero_slot: 0,
         slot_length: 1000,
     };
 
@@ -659,6 +662,7 @@ fn test_eval_3() {
 
     let slot_config = SlotConfig {
         zero_time: 1660003200000, // Preview network
+        zero_slot: 0,
         slot_length: 1000,
     };
 
@@ -925,6 +929,7 @@ fn test_eval_4() {
 
     let slot_config = SlotConfig {
         zero_time: 1660003200000, // Preview network
+        zero_slot: 0,
         slot_length: 1000,
     };
 
@@ -1006,6 +1011,7 @@ fn test_eval_5() {
 
     let slot_config = SlotConfig {
         zero_time: 1660003200000, // Preview network
+        zero_slot: 0,
         slot_length: 1000,
     };
 
@@ -1108,6 +1114,7 @@ fn test_eval_6() {
 
     let slot_config = SlotConfig {
         zero_time: 1596059091000, // Mainnet network
+        zero_slot: 4492800,
         slot_length: 1000,
     };
 
@@ -1211,6 +1218,7 @@ fn test_eval_7() {
 
     let slot_config = SlotConfig {
         zero_time: 1596059091000, // Mainnet network
+        zero_slot: 4492800,
         slot_length: 1000,
     };
 
@@ -1301,6 +1309,7 @@ fn test_eval_8() {
 
     let slot_config = SlotConfig {
         zero_time: 1596059091000, // Mainnet network
+        zero_slot: 4492800,
         slot_length: 1000,
     };
 
@@ -1564,6 +1573,7 @@ fn eval_missing_redeemer() {
 
     let slot_config = SlotConfig {
         zero_time: 1660003200000, // Preview network
+        zero_slot: 0,
         slot_length: 1000,
     };
 
@@ -1642,6 +1652,7 @@ fn eval_extraneous_redeemer() {
 
     let slot_config = SlotConfig {
         zero_time: 1660003200000, // Preview network
+        zero_slot: 0,
         slot_length: 1000,
     };