diff --git a/changes.d/7024.feat.md b/changes.d/7024.feat.md
new file mode 100644
index 00000000000..78f790b3ad4
--- /dev/null
+++ b/changes.d/7024.feat.md
@@ -0,0 +1 @@
+Ensure `next()/previous()` syntax works for the `cylc play --startcp` option.
diff --git a/cylc/flow/config.py b/cylc/flow/config.py
index df5d7026a8d..f68f0331cc2 100644
--- a/cylc/flow/config.py
+++ b/cylc/flow/config.py
@@ -42,6 +42,7 @@
     Dict,
     Iterable,
     List,
+    Literal,
     Mapping,
     Optional,
     Set,
@@ -249,6 +250,17 @@ def interpolate_template(tmpl, params_dict):
         raise ParamExpandError('bad template syntax') from None
 
 
+def _parse_iso_cycle_point(value: str) -> str:
+    """Helper for parsing initial/start cycle point option in
+    datetime cycling mode."""
+    if value == 'now':
+        return get_current_time_string()
+    try:
+        return ingest_time(value, get_current_time_string())
+    except IsodatetimeError as exc:
+        raise WorkflowConfigError(str(exc)) from None
+
+
 class WorkflowConfig:
     """Class for workflow configuration items and derived quantities."""
 
@@ -468,7 +480,9 @@ def __init__(
 
         # after the call to init_cyclers, we can start getting proper points.
         init_cyclers(self.cfg)
-        self.cycling_type = get_interval_cls().get_null().TYPE
+        self.cycling_type: Literal['integer', 'iso8601'] = (
+            get_interval_cls().get_null().TYPE
+        )
         self.cycle_point_dump_format = get_dump_format(self.cycling_type)
 
         # Initial point from workflow definition (or CLI override above).
@@ -756,17 +770,11 @@ def process_initial_cycle_point(self) -> None:
             if orig_icp is None:
                 orig_icp = '1'
             icp = orig_icp
-        elif self.cycling_type == ISO8601_CYCLING_TYPE:
+        else:
             if orig_icp is None:
                 raise WorkflowConfigError(
                     "This workflow requires an initial cycle point.")
-            if orig_icp == "now":
-                icp = get_current_time_string()
-            else:
-                try:
-                    icp = ingest_time(orig_icp, get_current_time_string())
-                except IsodatetimeError as exc:
-                    raise WorkflowConfigError(str(exc)) from None
+            icp = _parse_iso_cycle_point(orig_icp)
         self.evaluated_icp = None
         if icp != orig_icp:
             # now/next()/previous() was used, need to store
@@ -807,8 +815,7 @@ def process_start_cycle_point(self) -> None:
             )
         if startcp:
             # Start from a point later than initial point.
-            if self.options.startcp == 'now':
-                self.options.startcp = get_current_time_string()
+            self.options.startcp = _parse_iso_cycle_point(startcp)
             self.start_point = get_point(self.options.startcp).standardise()
         elif starttask:
             # Start from designated task(s).
diff --git a/cylc/flow/option_parsers.py b/cylc/flow/option_parsers.py
index 95b6313b217..e460e6cfc77 100644
--- a/cylc/flow/option_parsers.py
+++ b/cylc/flow/option_parsers.py
@@ -123,10 +123,11 @@ def _update_sources(self, other):
 ICP_OPTION = OptionSettings(
     ["--initial-cycle-point", "--icp"],
     help=(
-        "Set the initial cycle point."
-        " Required if not defined in flow.cylc."
-        "\nMay be either an absolute point or an offset: See"
-        f" {SHORTLINK_TO_ICP_DOCS} (Cylc documentation link)."
+        "Set the initial cycle point. "
+        "Required if not defined in flow.cylc.\n"
+        "Can be an absolute point or an offset relative to the "
+        "current time - see "
+        f"{SHORTLINK_TO_ICP_DOCS} (Cylc documentation link)."
     ),
     metavar="CYCLE_POINT or OFFSET",
     action='store',
diff --git a/cylc/flow/scheduler_cli.py b/cylc/flow/scheduler_cli.py
index af55f66d2ed..8c08d7e4962 100644
--- a/cylc/flow/scheduler_cli.py
+++ b/cylc/flow/scheduler_cli.py
@@ -15,7 +15,6 @@
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 """Common logic for "cylc play" CLI."""
 
-from ansimarkup import parse as cparse
 import asyncio
 from copy import deepcopy
 from functools import lru_cache
@@ -24,50 +23,62 @@
 from pathlib import Path
 from shlex import quote
 import sys
-from typing import TYPE_CHECKING, Tuple
+from typing import (
+    TYPE_CHECKING,
+    Tuple,
+)
 
+from ansimarkup import parse as cparse
 from packaging.version import Version
 
-from cylc.flow import LOG, __version__
+from cylc.flow import (
+    LOG,
+    __version__,
+)
 from cylc.flow.exceptions import (
     CylcError,
     ServiceFileError,
     WorkflowStopped,
 )
-from cylc.flow.scripts.ping import run as cylc_ping
 import cylc.flow.flags
-from cylc.flow.id import upgrade_legacy_ids
 from cylc.flow.host_select import select_workflow_host
 from cylc.flow.hostuserutil import is_remote_host
+from cylc.flow.id import upgrade_legacy_ids
 from cylc.flow.id_cli import parse_ids_async
 from cylc.flow.loggingutil import (
-    close_log,
     RotatingLogFileHandler,
+    close_log,
 )
 from cylc.flow.network.client import WorkflowRuntimeClient
 from cylc.flow.network.log_stream_handler import ProtobufStreamHandler
 from cylc.flow.option_parsers import (
+    ICP_OPTION,
+    SHORTLINK_TO_ICP_DOCS,
     WORKFLOW_ID_ARG_DOC,
     CylcOptionParser as COP,
-    OptionSettings,
     Options,
-    ICP_OPTION,
+    OptionSettings,
 )
 from cylc.flow.pathutil import get_workflow_run_scheduler_log_path
 from cylc.flow.remote import cylc_server_cmd
-from cylc.flow.scheduler import Scheduler, SchedulerError
-from cylc.flow.scripts.common import cylc_header
 from cylc.flow.run_modes import WORKFLOW_RUN_MODES
-from cylc.flow.workflow_db_mgr import WorkflowDatabaseManager
-from cylc.flow.workflow_files import (
-    SUITERC_DEPR_MSG,
-    get_workflow_srv_dir,
+from cylc.flow.scheduler import (
+    Scheduler,
+    SchedulerError,
 )
+from cylc.flow.scripts.common import cylc_header
+from cylc.flow.scripts.ping import run as cylc_ping
 from cylc.flow.terminal import (
     cli_function,
     is_terminal,
     prompt,
 )
+from cylc.flow.workflow_db_mgr import WorkflowDatabaseManager
+from cylc.flow.workflow_files import (
+    SUITERC_DEPR_MSG,
+    get_workflow_srv_dir,
+)
+
 
 if TYPE_CHECKING:
     from optparse import Values
@@ -162,10 +173,14 @@
     OptionSettings(
         ["--start-cycle-point", "--startcp"],
         help=(
-            "Set the start cycle point, which may be after"
-            " the initial cycle point. If the specified start point is"
-            " not in the sequence, the next on-sequence point will"
-            " be used. (Not to be confused with the initial cycle point)"),
+            "Set the start cycle point, which may be after "
+            "the initial cycle point. "
+            "If the specified start point is not in the sequence, the next "
+            "on-sequence point will be used.\n"
+            "Can be an absolute point or an offset relative to the "
+            "current time, like the --initial-cycle-point option - see "
+            f"{SHORTLINK_TO_ICP_DOCS} (Cylc documentation link)."
+        ),
         metavar="CYCLE_POINT",
         action='store',
         dest="startcp",
diff --git a/tests/unit/test_config.py b/tests/unit/test_config.py
index eb236d7240b..74a711df7c6 100644
--- a/tests/unit/test_config.py
+++ b/tests/unit/test_config.py
@@ -314,6 +314,14 @@ def test_family_inheritance_and_quotes(
             None,
             id="ICP = now"
         ),
+        pytest.param(
+            ISO8601_CYCLING_TYPE,
+            {'initial cycle point': 'previous(T00)'},
+            '20050102T0000+0530',
+            '20050102T0000+0530',
+            None,
+            id="ICP = prev"
+        ),
         pytest.param(
             ISO8601_CYCLING_TYPE,
             {
@@ -413,6 +421,12 @@ def test_process_icp(
             '20050102T0615+0530',
             None
         ),
+        (
+            'previous(T00)',
+            None,
+            '20050102T0000+0530',
+            None,
+        ),
         (
             None,
             None,