diff --git a/ogusa/growfactor_update.py b/ogusa/growfactor_update.py
new file mode 100644
index 00000000..a7c0f614
--- /dev/null
+++ b/ogusa/growfactor_update.py
@@ -0,0 +1,168 @@
+import numpy as np
+import pandas as pd
+import os
+from ogcore.utils import safe_read_pickle
+
+# Relate OG output variables to grow factors
+GROWFACTOR_MAPPING = {
+    "ABOOK": "corp_profits",
+    "ASCHCI": "Y",
+    "ASCHCL": "Y",
+    "ASCHF": "Y",
+    "ATXPY": "personal_income",
+    "ACGNS": "hh_capital_income",
+    "ADIVS": "hh_capital_income",
+    "AIPD": "interest_income",
+    "AINTS": "interest_income",
+    "AWAGE": "wages_paid",
+    "ASOCSEC": "w",
+}
+
+
+def growth_rate_diff(base, reform):
+    """
+    This function calculates the difference in growth rates between the
+    base and reform policy scenarios.
+
+    Args:
+        base (DataFrame): DataFrame containing the base policy scenario
+        reform (DataFrame): DataFrame containing the reform policy scenario
+
+    Returns:
+        growth_diff (DataFrame): The difference in growth rates between
+            the base and reform policy scenarios
+    """
+    # Calculate the growth rates for the base and reform policy scenarios
+    base_growth = base.pct_change()
+    reform_growth = reform.pct_change()
+
+    # Calculate the difference in growth rates
+    growth_diff = reform_growth - base_growth
+    # Calculate the level shift in the first year
+    level_shift = (reform.iloc[0] - base.iloc[0]) / base.iloc[0]
+    # shift index back one so year is the year of the growth rate
+    growth_diff.index = growth_diff.index - 1
+    # Drop index 2024
+    growth_diff = growth_diff.drop(2024)
+    # And add the level shift in the 1st year
+    growth_diff.iloc[0] += level_shift
+
+    return growth_diff
+
+
+def compute_input_vars(tpi_dict, start_year, T):
+    """
+    This function takes a dictionary of output from OG-Core and computes
+    the variables necessary for a mapping to the series used to
+    compute grow factors.
+
+    Args:
+        tpi_dict (dict): Dictionary of output from OG-Core
+        start_year (int): The first year of the simulation
+        T (int): The number of years in the simulation
+
+    Returns:
+        df (DataFrame): DataFrame of input variables necessary for
+            computing grow factors
+
+    """
+
+    # make turn the dict into a DataFrame
+    tpi_filtered = {
+        k: v
+        for k, v in tpi_dict.items()
+        if k in ["Y", "r", "w", "B", "r_p", "L", "K_d"]
+    }
+    df = pd.DataFrame(
+        data=tpi_filtered, index=np.arange(start_year, start_year + T)
+    )
+
+    # Create some new variables:
+    df["corp_profits"] = df["Y"] - df["w"] * df["L"]
+    df["personal_income"] = df["w"] * df["L"] + df["r_p"] * df["B"]
+    df["hh_capital_income"] = df["r"] * df["K_d"]
+    df["interest_income"] = df["r_p"] * df["B"]
+    df["wages_paid"] = df["w"] * df["L"]
+
+    return df
+
+
+def update_growfactors(
+    tpi_base, tpi_reform, initial_growfactors, start_year=2025, T=320
+):
+    """
+    This function takes the output from OG-Core for the base and reform
+    policy scenarios and computes the difference in growth rates between
+    the two scenarios for the variables necessary for computing grow
+    factors. The function then updates the grow factors based on the
+    difference in growth rates.
+
+    Args:
+        tpi_base (dict): Dictionary of output from OG-Core for the base
+            policy scenario
+        tpi_reform (dict): Dictionary of output from OG-Core for the
+            reform policy scenario
+        initial_growfactors (DataFrame): Initial grow factors
+        start_year (int): The first year of the simulation
+        T (int): The number of years in the simulation
+
+    Returns:
+        updated_growfactors (DataFrame): Updated grow factors
+    """
+
+    # Compute the input variables for the base and reform policy scenarios
+    base = compute_input_vars(tpi_base, start_year, T)
+    reform = compute_input_vars(tpi_reform, start_year, T)
+
+    # Calculate the difference in growth rates between the base and
+    # reform policy scenarios
+    growth_diff = growth_rate_diff(base, reform)
+
+    # Keep only growth_diffs for years in the growfactors
+    max_year = growth_diff.index.max()
+    growth_diff = growth_diff.loc[start_year:max_year]
+
+    # Update the grow factors based on the difference in growth rates
+    updated_growfactors = initial_growfactors.copy()
+    for key, value in GROWFACTOR_MAPPING.items():
+        updated_growfactors.loc[start_year:, key] = initial_growfactors.loc[
+            start_year:, key
+        ] * (1 + growth_diff[value])
+
+    return updated_growfactors
+
+
+def update(base_sim_path, reform_sim_path, growfactor_path, output_path):
+    """
+    Takes paths for model output and grow factors and updates the
+    grow factors
+
+    Args:
+        base_sim_path (str): Path to the base policy scenario model output
+        reform_sim_path (str): Path to the reform policy scenario
+            model output
+        growfactor_path (str): Path to the initial grow factors
+        output_path (str): Path to save the updated grow factors
+
+    Returns:
+        None
+    """
+    tpi_base = safe_read_pickle(
+        os.path.join(base_sim_path, "TPI", "TPI_vars.pkl")
+    )
+    tpi_reform = safe_read_pickle(
+        os.path.join(reform_sim_path, "TPI", "TPI_vars.pkl")
+    )
+    base_params = safe_read_pickle(
+        os.path.join(base_sim_path, "model_params.pkl")
+    )
+    start_year = base_params.start_year
+    T = base_params.T
+
+    initial_growfactors = pd.read_csv(growfactor_path, index_col=0)
+
+    updated_growfactors = update_growfactors(
+        tpi_base, tpi_reform, initial_growfactors, start_year, T
+    )
+
+    updated_growfactors.to_csv(output_path)