diff --git a/freqtrade/exchange/exchange.py b/freqtrade/exchange/exchange.py
index abb03b86d..fe5561be2 100644
--- a/freqtrade/exchange/exchange.py
+++ b/freqtrade/exchange/exchange.py
@@ -793,9 +793,12 @@ def timeframe_to_msecs(ticker_interval: str) -> int:
     return ccxt.Exchange.parse_timeframe(ticker_interval) * 1000
 
 
-def timeframe_to_prev_date(timeframe: str, date: datetime = None):
+def timeframe_to_prev_date(timeframe: str, date: datetime = None) -> datetime:
     """
     Use Timeframe and determine last possible candle.
+    :param timeframe: timeframe in string format (e.g. "5m")
+    :param date: date to use. Defaults to utcnow()
+    :returns: date of previous candle (with utc timezone)
     """
     if not date:
         date = datetime.utcnow()
@@ -807,9 +810,12 @@ def timeframe_to_prev_date(timeframe: str, date: datetime = None):
     return datetime.fromtimestamp(new_timestamp, tz=timezone.utc)
 
 
-def timeframe_to_next_date(timeframe: str, date: datetime = None):
+def timeframe_to_next_date(timeframe: str, date: datetime = None) -> datetime:
     """
     Use Timeframe and determine next candle.
+    :param timeframe: timeframe in string format (e.g. "5m")
+    :param date: date to use. Defaults to utcnow()
+    :returns: date of next candle (with utc timezone)
     """
     if not date:
         date = datetime.utcnow()
diff --git a/freqtrade/tests/exchange/test_exchange.py b/freqtrade/tests/exchange/test_exchange.py
index e342af604..23604f44f 100644
--- a/freqtrade/tests/exchange/test_exchange.py
+++ b/freqtrade/tests/exchange/test_exchange.py
@@ -1571,45 +1571,41 @@ def test_timeframe_to_prev_date():
     # 2019-08-12 13:22:08
     date = datetime.fromtimestamp(1565616128, tz=timezone.utc)
 
-    # 5m -> 2019-08-12 13:20:00
-    assert timeframe_to_prev_date("5m", date) == datetime(
-        2019, 8, 12, 13, 20, 0, tzinfo=timezone.utc)
-    # 10m -> 2019-08-12 13:20:00
-    assert timeframe_to_prev_date("10m", date) == datetime(
-        2019, 8, 12, 13, 20, 0, tzinfo=timezone.utc)
-    # 1h -> 2019-08-12 13:00:00
-    assert timeframe_to_prev_date("1h", date) == datetime(
-        2019, 8, 12, 13, 00, 0, tzinfo=timezone.utc)
-    # 2h -> 2019-08-12 12:00:00
-    assert timeframe_to_prev_date("2h", date) == datetime(
-        2019, 8, 12, 12, 00, 0, tzinfo=timezone.utc)
-    # 4h -> 2019-08-12 12:00:00
-    assert timeframe_to_prev_date("4h", date) == datetime(
-        2019, 8, 12, 12, 00, 0, tzinfo=timezone.utc)
-    # 1d -> 2019-08-12 00:00:00
-    assert timeframe_to_prev_date("1d", date) == datetime(
-        2019, 8, 12, 0, 0, 0, tzinfo=timezone.utc)
+    tf_list = [
+        # 5m -> 2019-08-12 13:20:00
+        ("5m", datetime(2019, 8, 12, 13, 20, 0, tzinfo=timezone.utc)),
+        # 10m -> 2019-08-12 13:20:00
+        ("10m", datetime(2019, 8, 12, 13, 20, 0, tzinfo=timezone.utc)),
+        # 1h -> 2019-08-12 13:00:00
+        ("1h", datetime(2019, 8, 12, 13, 00, 0, tzinfo=timezone.utc)),
+        # 2h -> 2019-08-12 12:00:00
+        ("2h", datetime(2019, 8, 12, 12, 00, 0, tzinfo=timezone.utc)),
+        # 4h -> 2019-08-12 12:00:00
+        ("4h", datetime(2019, 8, 12, 12, 00, 0, tzinfo=timezone.utc)),
+        # 1d -> 2019-08-12 00:00:00
+        ("1d", datetime(2019, 8, 12, 00, 00, 0, tzinfo=timezone.utc)),
+    ]
+    for interval, result in tf_list:
+        assert timeframe_to_prev_date(interval, date) == result
 
 
 def test_timeframe_to_next_date():
     # 2019-08-12 13:22:08
     date = datetime.fromtimestamp(1565616128, tz=timezone.utc)
+    tf_list = [
+        # 5m -> 2019-08-12 13:25:00
+        ("5m", datetime(2019, 8, 12, 13, 25, 0, tzinfo=timezone.utc)),
+        # 10m -> 2019-08-12 13:30:00
+        ("10m", datetime(2019, 8, 12, 13, 30, 0, tzinfo=timezone.utc)),
+        # 1h -> 2019-08-12 14:00:00
+        ("1h", datetime(2019, 8, 12, 14, 00, 0, tzinfo=timezone.utc)),
+        # 2h -> 2019-08-12 14:00:00
+        ("2h", datetime(2019, 8, 12, 14, 00, 0, tzinfo=timezone.utc)),
+        # 4h -> 2019-08-12 14:00:00
+        ("4h", datetime(2019, 8, 12, 16, 00, 0, tzinfo=timezone.utc)),
+        # 1d -> 2019-08-13 00:00:00
+        ("1d", datetime(2019, 8, 13, 0, 0, 0, tzinfo=timezone.utc)),
+    ]
 
-    # 5m -> 2019-08-12 13:25:00
-    assert timeframe_to_next_date("5m", date) == datetime(
-        2019, 8, 12, 13, 25, 0, tzinfo=timezone.utc)
-    # 10m -> 2019-08-12 13:30:00
-    assert timeframe_to_next_date("10m", date) == datetime(
-        2019, 8, 12, 13, 30, 0, tzinfo=timezone.utc)
-    # 1h -> 2019-08-12 14:00:00
-    assert timeframe_to_next_date("1h", date) == datetime(
-        2019, 8, 12, 14, 00, 0, tzinfo=timezone.utc)
-    # 2h -> 2019-08-12 14:00:00
-    assert timeframe_to_next_date("2h", date) == datetime(
-        2019, 8, 12, 14, 00, 0, tzinfo=timezone.utc)
-    # 4h -> 2019-08-12 14:00:00
-    assert timeframe_to_next_date("4h", date) == datetime(
-        2019, 8, 12, 16, 00, 0, tzinfo=timezone.utc)
-    # 1d -> 2019-08-13 00:00:00
-    assert timeframe_to_next_date("1d", date) == datetime(
-        2019, 8, 13, 0, 0, 0, tzinfo=timezone.utc)
+    for interval, result in tf_list:
+        assert timeframe_to_next_date(interval, date) == result