diff --git a/src/forward_link.py b/src/forward_link.py
new file mode 100644
index 00000000..1ac97429
--- /dev/null
+++ b/src/forward_link.py
@@ -0,0 +1,76 @@
+import numpy as np
+import pandas as pd
+
+
+def calculate_imputation_link(
+    df: pd.DataFrame,
+    period: str,
+    strata: str,
+    match_col: str,
+    target_variable: str,
+    predictive_variable: str,
+) -> pd.DataFrame:
+    """
+    Calculate link between target_variable and predictive_variable by strata,
+    a match_col must be supplied which indicates if target_variable
+    and predictive_variable can be linked.
+
+    Parameters
+    ----------
+    df : pd.Dataframe
+        Original dataframe.
+    period : str
+        Column name containing time period.
+    strata : str
+        Column name containing strata information (sic).
+    match_col : str
+        Column name of the matched pair links, this column should be bool.
+    target_variable : str
+        Column name of the targeted variable.
+    predictive_variable : str
+        Column name of the predicted target variable.
+
+    Returns
+    -------
+    df : pd.DataFrame
+        A pandas DataFrame with a new column containing either f_link or b_link
+        based on the input parameters.
+    """
+
+    df_intermediate = df.copy()
+
+    if match_col == "f_matched_pair" and predictive_variable == "f_predictive_question":
+        link_col_name = "f_link"
+
+    elif (
+        match_col == "b_matched_pair" and predictive_variable == "b_predictive_question"
+    ):
+        link_col_name = "b_link"
+
+    else:
+        raise ValueError(
+            f"""
+        {match_col} and {predictive_variable} do not have same wildcard."""
+        )
+
+    df_intermediate[target_variable] = (
+        df_intermediate[target_variable] * df_intermediate[match_col]
+    )
+
+    df_intermediate[predictive_variable] = (
+        df_intermediate[predictive_variable] * df_intermediate[match_col]
+    )
+
+    numerator = df_intermediate.groupby([strata, period])[target_variable].transform(
+        "sum"
+    )
+
+    denominator = df_intermediate.groupby([strata, period])[
+        predictive_variable
+    ].transform("sum")
+
+    denominator.replace(0, np.nan, inplace=True)  # cover division with 0
+
+    df[link_col_name] = numerator / denominator
+
+    return df
diff --git a/tests/calculate_links_test_data.csv b/tests/calculate_links_test_data.csv
new file mode 100755
index 00000000..72e6408d
--- /dev/null
+++ b/tests/calculate_links_test_data.csv
@@ -0,0 +1,16 @@
+,identifier,period,group,question,f_predictive_question,b_predictive_question,f_matched_pair,b_matched_pair,f_link,b_link
+0,10001,202001,1,547.0,,362.0,False,True,,0.9925133689839573
+1,10001,202002,1,362.0,547.0,895.0,True,True,1.0075431034482758,0.8431018935978359
+2,10001,202003,1,895.0,362.0,,True,False,1.186096256684492,
+3,10002,202001,1,381.0,,573.0,False,True,,0.9925133689839573
+4,10002,202002,1,573.0,381.0,214.0,True,True,1.0075431034482758,0.8431018935978359
+5,10002,202003,1,214.0,573.0,,True,False,1.186096256684492,
+6,10001,202001,2,961.0,,267.0,False,True,,1.693854748603352
+7,10001,202002,2,267.0,961.0,314.0,True,True,0.5903693931398417,0.8523809523809524
+8,10001,202003,2,314.0,267.0,,True,False,1.1731843575418994,
+9,10002,202001,2,555.0,,628.0,False,True,,1.693854748603352
+10,10002,202002,2,628.0,555.0,736.0,True,True,0.5903693931398417,0.8523809523809524
+11,10002,202003,2,736.0,628.0,,True,False,1.1731843575418994,
+12,10005,202001,1,,,,False,False,,0.9925133689839573
+13,10005,202002,2,,,100.0,False,False,0.5903693931398417,0.8523809523809524
+14,10005,202003,2,100.0,,,False,False,1.1731843575418994,
diff --git a/tests/test_forward_link.py b/tests/test_forward_link.py
new file mode 100644
index 00000000..51fa63c8
--- /dev/null
+++ b/tests/test_forward_link.py
@@ -0,0 +1,75 @@
+import pytest
+from helper_functions import load_and_format
+from pandas.testing import assert_frame_equal
+
+from src.forward_link import calculate_imputation_link
+
+scenarios = ["calculate_links_test_data"]
+
+
+@pytest.mark.parametrize("scenario", scenarios)
+class TestLinks:
+    def test_forward_links(self, scenario):
+        """Test if function returns the f_link column"""
+
+        df_output = load_and_format("tests/" + scenario + ".csv")
+
+        df_input = df_output.drop(columns=["f_link"])
+
+        df_input = calculate_imputation_link(
+            df_input,
+            "period",
+            "group",
+            "f_matched_pair",
+            "question",
+            "f_predictive_question",
+        )
+
+        assert_frame_equal(df_input, df_output, check_like=True)
+
+    def test_back_links(self, scenario):
+        """Test if function returns the b_link column"""
+        df_output = load_and_format("tests/" + scenario + ".csv")
+
+        df_input = df_output.drop(columns=["b_link"])
+
+        df_input = calculate_imputation_link(
+            df_input,
+            "period",
+            "group",
+            "b_matched_pair",
+            "question",
+            "b_predictive_question",
+        )
+
+        assert_frame_equal(df_input, df_output, check_like=True)
+
+    def test_exception(self, scenario):
+
+        df = load_and_format("tests/" + scenario + ".csv")
+
+        with pytest.raises(ValueError):
+            """
+            Test if function is called with wrong arguments, in particular
+            with f_matched_pair and b_predictive_question or with
+            b_matched_pair and f_predictive_question.
+            """
+
+            df = calculate_imputation_link(
+                df,
+                "period",
+                "group",
+                "f_matched_pair",
+                "question",
+                "b_predictive_question",
+            )
+        with pytest.raises(ValueError):
+
+            df = calculate_imputation_link(
+                df,
+                "period",
+                "group",
+                "b_matched_pair",
+                "question",
+                "f_predictive_question",
+            )