diff --git a/src/toldg/models.py b/src/toldg/models.py
index 5a96df6..ee4832d 100644
--- a/src/toldg/models.py
+++ b/src/toldg/models.py
@@ -40,8 +40,6 @@ class Config(BaseModel):
         categories (List[str]):  A list of account2s. An account has to be defined here
                                  before it can be used in a mapping. Otherwise, ledger will complain.
         commodities (List[str]): A list of commodities relevant to the data processing.
-        find_duplicates (bool):  Flag to check and abort on duplicated transactions. Not
-                                 really useful.
     """
 
     class Config:
@@ -52,7 +50,6 @@ class Config(BaseModel):
     output_file: Path = Path("output.ldg")
     csv_configs: List[CsvConfig]
     categories: List[str]
-    find_duplicates: bool = False
 
 
 class Transaction(BaseModel):
@@ -81,5 +78,6 @@ class Mapping(BaseModel):
         extra = "forbid"
 
     account2: str
+    count: int = 1
     narration: Optional[str] = None
     payee: Optional[str] = None
diff --git a/src/toldg/process.py b/src/toldg/process.py
index f9443b4..a04802f 100644
--- a/src/toldg/process.py
+++ b/src/toldg/process.py
@@ -64,29 +64,16 @@ def get_transactions(csv_file: str, config: CsvConfig) -> List[Transaction]:
     return transactions
 
 
-def find_duplicates(transactions: List[Transaction]):
-    rows = set()
-    for t in transactions:
-        row = t.row
-        if row in rows:
-            logging.critical(f"'{row}' is duplicated.")
-            logging.critical("Exit because of duplicated transactions.")
-            sys.exit(1)
-        else:
-            rows.add(row)
-
-
 def apply_mappings(transactions: List[Transaction], mappings: Dict[str, Mapping]):
     """Apply mappings to transactions."""
-    unused_mappings = set(mappings.keys())
-
     for t in transactions:
         if t.row in mappings:
             mapping = mappings[t.row]
-
-            assert isinstance(
-                mapping, Mapping
-            ), "Only new mappings format is supported."
+            assert isinstance(mapping, Mapping)
+            assert (
+                mapping.count > 0
+            ), f"{mapping} used by {t} but count is not greater than '0'."
+            mapping.count -= 1
             t.account2 = mapping.account2
 
             if mapping.narration:
@@ -94,15 +81,11 @@ def apply_mappings(transactions: List[Transaction], mappings: Dict[str, Mapping]
 
             if mapping.payee:
                 t.payee = mapping.payee
-
-            unused_mappings.discard(t.row)
         else:
             logging.warning(f"No mapping for '{t}'.")
 
-    for row in unused_mappings:
-        mapping_info = mappings[row]
-        account2 = mapping_info["account2"]
-        logging.warning(f"Unused mapping '{row}' -> {account2}")
+    for mapping in mappings.values():
+        assert mapping.count == 0, f"{mapping} was not used as often as expected!"
 
 
 def process_csv_files(config: Config):
@@ -113,9 +96,6 @@ def process_csv_files(config: Config):
         csv_config = get_csv_config(csv_file, config.csv_configs)
         transactions += get_transactions(csv_file, csv_config)
 
-    if config.find_duplicates:
-        find_duplicates(transactions)
-
     mappings = toldg.utils.read_mappings(config.mappings_file)
     apply_mappings(transactions, mappings)
     toldg.predict.add_account2(transactions, config.categories)
diff --git a/src/toldg/utils.py b/src/toldg/utils.py
index 034964c..07e30b4 100644
--- a/src/toldg/utils.py
+++ b/src/toldg/utils.py
@@ -67,19 +67,21 @@ def write_meta(config: Config):
 
 def write_mappings(transactions: List[Transaction], mappings_file: Path):
     """Write transactions to the mappings file."""
-    mappings = {}
-    for t in transactions:
-        mapping = Mapping(
-            **{
-                "account2": t.account2.strip(),
-            }
-        )
-        if t.narration:
-            mapping.narration = t.narration
-        if t.payee:
-            mapping.payee = t.payee
-        mappings[t.row] = mapping.dict()
 
+    mappings = read_mappings(mappings_file)
+    for t in transactions:
+        if t.row in mappings:
+            pass
+        else:
+            mapping = Mapping(
+                **{
+                    "account2": t.account2.strip(),
+                    "narration": t.description,
+                }
+            )
+            mappings[t.row] = mapping
+
+    mappings = {k: v.dict() for k, v in mappings.items()}
     with open(mappings_file, "w") as f:
         json.dump(mappings, f, indent=4)