diff --git a/postgres/assignments.sql.go b/postgres/assignments.sql.go
index 52bd45d..633b6d0 100644
--- a/postgres/assignments.sql.go
+++ b/postgres/assignments.sql.go
@@ -148,3 +148,22 @@ func (q *Queries) UpdateAssignment(ctx context.Context, arg UpdateAssignmentPara
 	_, err := q.db.ExecContext(ctx, updateAssignment, arg.CategoryID, arg.Date, arg.Amount)
 	return err
 }
+
+const updateAssignmentWithDifference = `-- name: UpdateAssignmentWithDifference :exec
+INSERT INTO assignments (category_id, date, amount)
+VALUES($1, $2, $3) 
+ON CONFLICT (category_id, date) 
+DO 
+   UPDATE SET amount = assignments.amount + $3
+`
+
+type UpdateAssignmentWithDifferenceParams struct {
+	CategoryID uuid.UUID
+	Date       time.Time
+	Amount     numeric.Numeric
+}
+
+func (q *Queries) UpdateAssignmentWithDifference(ctx context.Context, arg UpdateAssignmentWithDifferenceParams) error {
+	_, err := q.db.ExecContext(ctx, updateAssignmentWithDifference, arg.CategoryID, arg.Date, arg.Amount)
+	return err
+}
diff --git a/postgres/queries/assignments.sql b/postgres/queries/assignments.sql
index cb0687d..145eee7 100644
--- a/postgres/queries/assignments.sql
+++ b/postgres/queries/assignments.sql
@@ -29,4 +29,11 @@ INSERT INTO assignments (category_id, date, amount)
 VALUES($1, $2, $3) 
 ON CONFLICT (category_id, date) 
 DO 
-   UPDATE SET amount = $3;
\ No newline at end of file
+   UPDATE SET amount = $3;
+
+-- name: UpdateAssignmentWithDifference :exec
+INSERT INTO assignments (category_id, date, amount)
+VALUES($1, $2, $3) 
+ON CONFLICT (category_id, date) 
+DO 
+   UPDATE SET amount = assignments.amount + $3;
\ No newline at end of file
diff --git a/postgres/ynab-import.go b/postgres/ynab-import.go
index 83c5f9d..13f6afa 100644
--- a/postgres/ynab-import.go
+++ b/postgres/ynab-import.go
@@ -91,12 +91,12 @@ func (ynab *YNABImport) ImportAssignments(context context.Context, r io.Reader)
 			continue
 		}
 
-		assignment := CreateAssignmentParams{
+		assignment := UpdateAssignmentWithDifferenceParams{
 			Date:       date,
 			CategoryID: category.UUID,
 			Amount:     amount,
 		}
-		_, err = ynab.queries.CreateAssignment(context, assignment)
+		err = ynab.queries.UpdateAssignmentWithDifference(context, assignment)
 		if err != nil {
 			return fmt.Errorf("save assignment %v: %w", assignment, err)
 		}
@@ -226,7 +226,8 @@ func (ynab *YNABImport) GetTransaction(context context.Context, record []string)
 }
 
 func (ynab *YNABImport) ImportRegularTransaction(context context.Context, payeeName string,
-	transaction CreateTransactionParams) error {
+	transaction CreateTransactionParams,
+) error {
 	payeeID, err := ynab.GetPayee(context, payeeName)
 	if err != nil {
 		return fmt.Errorf("get payee %s: %w", payeeName, err)
@@ -242,7 +243,8 @@ func (ynab *YNABImport) ImportRegularTransaction(context context.Context, payeeN
 
 func (ynab *YNABImport) ImportTransferTransaction(context context.Context, payeeName string,
 	transaction CreateTransactionParams, openTransfers *[]Transfer,
-	account *Account, amount numeric.Numeric) error {
+	account *Account, amount numeric.Numeric,
+) error {
 	transferToAccountName := payeeName[11:]
 	transferToAccount, err := ynab.GetAccount(context, transferToAccountName)
 	if err != nil {