diff --git a/src/pricehist/format.py b/src/pricehist/format.py
index 0c9dcbe..64519f7 100644
--- a/src/pricehist/format.py
+++ b/src/pricehist/format.py
@@ -1,5 +1,4 @@
 from dataclasses import dataclass
-from decimal import Decimal, getcontext
 
 
 @dataclass(frozen=True)
@@ -9,3 +8,9 @@ class Format:
     thousands: str = ""
     symbol: str = "rightspace"
     datesep: str = "-"
+
+    def format_num(self, num):
+        parts = f"{num:,}".split(".")
+        parts[0] = parts[0].replace(",", self.thousands)
+        result = self.decimal.join(parts)
+        return result
diff --git a/src/pricehist/outputs/beancount.py b/src/pricehist/outputs/beancount.py
index 73bc2ef..13b9980 100644
--- a/src/pricehist/outputs/beancount.py
+++ b/src/pricehist/outputs/beancount.py
@@ -8,9 +8,8 @@ class Beancount(BaseOutput):
         lines = []
         for price in series.prices:
 
-            amount_parts = f"{price.amount:,}".split(".")
-            amount_parts[0] = amount_parts[0].replace(",", fmt.thousands)
-            amount = ".".join(amount_parts)
+            amount = fmt.format_num(price.amount)
+            # TODO warn if fmt settings make an invalid number
 
             qa_parts = [amount]
             if fmt.symbol == "right":
diff --git a/src/pricehist/outputs/csv.py b/src/pricehist/outputs/csv.py
index 93013e8..b34aacb 100644
--- a/src/pricehist/outputs/csv.py
+++ b/src/pricehist/outputs/csv.py
@@ -8,9 +8,7 @@ class CSV(BaseOutput):
         lines = ["date,base,quote,amount,source,type"]
         for price in series.prices:
             date = str(price.date).replace("-", fmt.datesep)
-            amount_parts = f"{price.amount:,}".split(".")
-            amount_parts[0] = amount_parts[0].replace(",", fmt.thousands)
-            amount = fmt.decimal.join(amount_parts)
+            amount = fmt.format_num(price.amount)
             line = ",".join(
                 [date, series.base, series.quote, amount, source.id(), series.type]
             )
diff --git a/src/pricehist/outputs/gnucashsql.py b/src/pricehist/outputs/gnucashsql.py
index 61b40cc..bd29b17 100644
--- a/src/pricehist/outputs/gnucashsql.py
+++ b/src/pricehist/outputs/gnucashsql.py
@@ -29,6 +29,7 @@ class GnuCashSQL(BaseOutput):
                 ).encode("utf-8")
             )
             guid = m.hexdigest()[0:32]
+            # TODO extract this logic to a helper method
             value_num = str(price.amount).replace(".", "")
             value_denom = 10 ** len(f"{price.amount}.".split(".")[1])
             v = (
diff --git a/src/pricehist/outputs/ledger.py b/src/pricehist/outputs/ledger.py
index 8271b49..dfe2d22 100644
--- a/src/pricehist/outputs/ledger.py
+++ b/src/pricehist/outputs/ledger.py
@@ -9,9 +9,7 @@ class Ledger(BaseOutput):
         for price in series.prices:
             date = str(price.date).replace("-", fmt.datesep)
 
-            amount_parts = f"{price.amount:,}".split(".")
-            amount_parts[0] = amount_parts[0].replace(",", fmt.thousands)
-            amount = fmt.decimal.join(amount_parts)
+            amount = fmt.format_num(price.amount)
 
             qa_parts = [amount]
             if fmt.symbol == "left":