diff --git a/routes/operations.js b/routes/operations.js
index ecf1d9d..385e6c0 100644
--- a/routes/operations.js
+++ b/routes/operations.js
@@ -123,18 +123,23 @@ module.exports = function(pool) {
 
     // load baseline rows from source table — additive, no delete
     router.post('/versions/:id/baseline', async (req, res) => {
-        const { where_clause, date_offset, pf_user, note } = req.body;
+        const { where_clause, date_offset, pf_user, note, filters } = req.body;
         const dateOffset    = date_offset  || '0 days';
         const filterClause  = (where_clause || '').trim() || 'TRUE';
         try {
             const ctx = await getContext(parseInt(req.params.id), 'baseline');
             if (!guardOpen(ctx.version, res)) return;
+            const paramsJson = JSON.stringify({
+                where_clause: filterClause,
+                date_offset:  dateOffset,
+                ...(filters ? { filters } : {})
+            });
             const sql = applyTokens(ctx.sql, {
                 fc_table:      ctx.table,
                 version_id:    ctx.version.id,
                 pf_user:       esc(pf_user || ''),
                 note:          esc(note    || ''),
-                params:        esc(JSON.stringify({ where_clause: filterClause, date_offset: dateOffset })),
+                params:        esc(paramsJson),
                 filter_clause: filterClause,
                 date_offset:   esc(dateOffset)
             });
@@ -147,6 +152,92 @@ module.exports = function(pool) {
         }
     });
 
+    // edit a baseline or reference segment in place — only allowed before any
+    // scale/recode/clone has been applied on this version, since those would
+    // have been calibrated against the old segment's totals.
+    router.put('/versions/:id/baseline/:logid', async (req, res) => {
+        const versionId = parseInt(req.params.id);
+        const logid     = parseInt(req.params.logid);
+        const { where_clause, date_offset, pf_user, note, filters } = req.body;
+        const dateOffset   = date_offset  || '0 days';
+        const filterClause = (where_clause || '').trim() || 'TRUE';
+
+        const client = await pool.connect();
+        try {
+            const logResult = await client.query(
+                `SELECT * FROM pf.log WHERE id = $1 AND version_id = $2`,
+                [logid, versionId]
+            );
+            if (logResult.rows.length === 0) {
+                return res.status(404).json({ error: 'Log entry not found' });
+            }
+            const oldLog = logResult.rows[0];
+            if (!['baseline', 'reference'].includes(oldLog.operation)) {
+                return res.status(400).json({ error: 'Only baseline or reference segments can be edited' });
+            }
+
+            const opsResult = await client.query(
+                `SELECT COUNT(*)::int AS n FROM pf.log
+                 WHERE version_id = $1 AND operation IN ('scale', 'recode', 'clone')`,
+                [versionId]
+            );
+            if (opsResult.rows[0].n > 0) {
+                return res.status(409).json({
+                    error: 'Cannot edit segments after forecast operations have been applied. Undo the operations first.'
+                });
+            }
+
+            const ctx = await getContext(versionId, oldLog.operation);
+            if (!guardOpen(ctx.version, res)) return;
+
+            const paramsJson = JSON.stringify({
+                where_clause: filterClause,
+                ...(oldLog.operation === 'baseline' ? { date_offset: dateOffset } : {}),
+                ...(filters ? { filters } : {})
+            });
+            const tokens = oldLog.operation === 'baseline'
+                ? {
+                    fc_table:      ctx.table,
+                    version_id:    ctx.version.id,
+                    pf_user:       esc(pf_user || ''),
+                    note:          esc(note    || ''),
+                    params:        esc(paramsJson),
+                    filter_clause: filterClause,
+                    date_offset:   esc(dateOffset)
+                }
+                : {
+                    fc_table:      ctx.table,
+                    version_id:    ctx.version.id,
+                    pf_user:       esc(pf_user || ''),
+                    note:          esc(note    || ''),
+                    params:        esc(paramsJson),
+                    filter_clause: filterClause
+                };
+            const sql = applyTokens(ctx.sql, tokens);
+
+            await client.query('BEGIN');
+            const delRows = await client.query(
+                `DELETE FROM ${ctx.table} WHERE pf_logid = $1 RETURNING pf_id`,
+                [logid]
+            );
+            await client.query(`DELETE FROM pf.log WHERE id = $1`, [logid]);
+            const insResult = await client.query(sql);
+            await client.query('COMMIT');
+
+            res.json({
+                rows_deleted: delRows.rowCount,
+                pf_ids:       delRows.rows.map(r => r.pf_id),
+                rows_affected: insResult.rows[0]?.rows_affected ?? 0
+            });
+        } catch (err) {
+            try { await client.query('ROLLBACK'); } catch {}
+            console.error(err);
+            res.status(err.status || 500).json({ error: err.message });
+        } finally {
+            client.release();
+        }
+    });
+
     // delete all baseline rows and log entries for a version
     router.delete('/versions/:id/baseline', async (req, res) => {
         const versionId = parseInt(req.params.id);
@@ -183,17 +274,21 @@ module.exports = function(pool) {
 
     // load reference rows from source table (additive — does not clear prior reference rows)
     router.post('/versions/:id/reference', async (req, res) => {
-        const { where_clause, pf_user, note } = req.body;
+        const { where_clause, pf_user, note, filters } = req.body;
         const filterClause = (where_clause || '').trim() || 'TRUE';
         try {
             const ctx = await getContext(parseInt(req.params.id), 'reference');
             if (!guardOpen(ctx.version, res)) return;
+            const paramsJson = JSON.stringify({
+                where_clause: filterClause,
+                ...(filters ? { filters } : {})
+            });
             const sql = applyTokens(ctx.sql, {
                 fc_table:      ctx.table,
                 version_id:    ctx.version.id,
                 pf_user:       esc(pf_user || ''),
                 note:          esc(note    || ''),
-                params:        esc(JSON.stringify({ where_clause: filterClause })),
+                params:        esc(paramsJson),
                 filter_clause: filterClause
             });
 
diff --git a/ui/src/views/Baseline.jsx b/ui/src/views/Baseline.jsx
index c49dcc0..745297d 100644
--- a/ui/src/views/Baseline.jsx
+++ b/ui/src/views/Baseline.jsx
@@ -73,6 +73,8 @@ export default function Baseline({ sources = [], sourceId, versions = [], versio
   const [offsetMo,       setOffsetMo]       = useState(0)
   const [segNote,        setSegNote]        = useState('')
   const [submitting,     setSubmitting]     = useState(false)
+  const [editingLogId,   setEditingLogId]   = useState(null)
+  const [hasForecastOps, setHasForecastOps] = useState(false)
 
   const [expandedId,     setExpandedId]     = useState(null)
   const [msg,            setMsg]            = useState(null)
@@ -94,6 +96,7 @@ export default function Baseline({ sources = [], sourceId, versions = [], versio
   function loadLog() {
     fetch(`/api/versions/${versionId}/log`).then(r => r.json()).then(data => {
       setLog(data.filter(e => e.operation === 'baseline' || e.operation === 'reference'))
+      setHasForecastOps(data.some(e => ['scale', 'recode', 'clone'].includes(e.operation)))
     })
   }
 
@@ -159,21 +162,26 @@ export default function Baseline({ sources = [], sourceId, versions = [], versio
     const offsetStr = isRef ? '0 days' : ([offsetYr > 0 ? `${offsetYr} year` : '', offsetMo > 0 ? `${offsetMo} month` : ''].filter(Boolean).join(' ') || '0 days')
     const endpoint = isRef ? 'reference' : 'baseline'
     const body = isRef
-      ? { where_clause: clause, pf_user: 'admin', note: description || segNote }
-      : { where_clause: clause, date_offset: offsetStr, pf_user: 'admin', note: description || segNote }
+      ? { where_clause: clause, pf_user: 'admin', note: description || segNote, filters }
+      : { where_clause: clause, date_offset: offsetStr, pf_user: 'admin', note: description || segNote, filters }
     setSubmitting(true)
     try {
-      const res = await fetch(`/api/versions/${versionId}/${endpoint}`, {
-        method: 'POST',
+      const url    = editingLogId
+        ? `/api/versions/${versionId}/baseline/${editingLogId}`
+        : `/api/versions/${versionId}/${endpoint}`
+      const method = editingLogId ? 'PUT' : 'POST'
+      const res = await fetch(url, {
+        method,
         headers: { 'Content-Type': 'application/json' },
         body: JSON.stringify(body)
       })
       const data = await res.json()
       if (!res.ok) { flash(data.error, 'error'); return }
-      flash(`Loaded ${data.rows_affected ?? data.row_count ?? ''} rows`)
+      flash(editingLogId
+        ? `Updated — ${data.rows_deleted} rows replaced with ${data.rows_affected}`
+        : `Loaded ${data.rows_affected ?? data.row_count ?? ''} rows`)
       loadLog()
-      setDescription(''); setSegNote(''); setOffsetYr(0); setOffsetMo(0)
-      setFilters(filterCols.length > 0 ? [emptyFilter(filterCols)] : [])
+      cancelEdit()
     } catch (err) {
       flash(err.message, 'error')
     } finally {
@@ -181,6 +189,47 @@ export default function Baseline({ sources = [], sourceId, versions = [], versio
     }
   }
 
+  function startEdit(entry) {
+    if (hasForecastOps) {
+      flash('Undo forecast operations first to edit segments', 'error')
+      return
+    }
+    const params = entry.params || {}
+    setSegType(entry.operation)
+    setSegNote(entry.note || '')
+    setDescription('')
+    if (entry.operation === 'baseline') {
+      const off = parseOffset(params.date_offset)
+      setOffsetYr(off.yr)
+      setOffsetMo(off.mo)
+    } else {
+      setOffsetYr(0); setOffsetMo(0)
+    }
+    if (Array.isArray(params.filters) && params.filters.length > 0) {
+      setFilters(params.filters)
+    } else if (filterCols.length > 0) {
+      // Pre-existing segment without structured filters — fall back to a blank row.
+      // The original WHERE clause is shown read-only on the segment detail row.
+      setFilters([emptyFilter(filterCols)])
+      flash('Filters were not stored on this segment — rebuild them, or undo and re-add', 'error')
+    }
+    setEditingLogId(entry.id)
+    setExpandedId(null)
+    setTimeout(() => {
+      const form = document.getElementById('add-segment')
+      form?.scrollIntoView({ behavior: 'smooth', block: 'start' })
+    }, 0)
+  }
+
+  function cancelEdit() {
+    setEditingLogId(null)
+    setDescription('')
+    setSegNote('')
+    setOffsetYr(0)
+    setOffsetMo(0)
+    setFilters(filterCols.length > 0 ? [emptyFilter(filterCols)] : [])
+  }
+
   async function undoSegment(logid) {
     await fetch(`/api/log/${logid}`, { method: 'DELETE' })
     loadLog()
@@ -331,6 +380,9 @@ export default function Baseline({ sources = [], sourceId, versions = [], versio
                         <td className="px-3 py-2 text-gray-500">{entry.pf_user}</td>
                         <td className="px-3 py-2 text-gray-400">{new Date(entry.stamp).toLocaleDateString()}</td>
                         <td className="px-3 py-2 text-right">
+                          {!hasForecastOps && (
+                            <button onClick={e => { e.stopPropagation(); startEdit(entry) }} className="text-gray-400 hover:text-blue-600 text-xs mr-3">Edit</button>
+                          )}
                           <button onClick={e => { e.stopPropagation(); undoSegment(entry.id) }} className="text-gray-400 hover:text-red-500 text-xs">Undo</button>
                         </td>
                       </tr>
@@ -362,10 +414,19 @@ export default function Baseline({ sources = [], sourceId, versions = [], versio
             </table>
           </div>
 
-          {/* Add Segment */}
-          <div className="bg-white border border-gray-200 rounded">
-            <div className="px-3 py-2 border-b border-gray-100 text-xs font-medium text-gray-500 uppercase tracking-wide">
-              Add Segment
+          {/* Add / Edit Segment */}
+          <div id="add-segment" className="bg-white border border-gray-200 rounded">
+            <div className="px-3 py-2 border-b border-gray-100 text-xs font-medium text-gray-500 uppercase tracking-wide flex items-center justify-between">
+              <span>{(() => {
+                if (!editingLogId) return 'Add Segment'
+                const entry = log.find(e => e.id === editingLogId)
+                if (!entry) return 'Edit Segment'
+                const label = entry.operation === 'reference' ? 'reference' : 'baseline'
+                return entry.note ? `Edit ${label} — ${entry.note}` : `Edit ${label} segment`
+              })()}</span>
+              {editingLogId && (
+                <button onClick={cancelEdit} className="text-gray-400 hover:text-gray-600 normal-case font-normal">Cancel edit</button>
+              )}
             </div>
             <div className="p-4 flex flex-col gap-4">
 
@@ -465,7 +526,11 @@ export default function Baseline({ sources = [], sourceId, versions = [], versio
                   <input value={segNote} onChange={e => setSegNote(e.target.value)} placeholder="optional" className="border border-gray-200 rounded px-2 py-1.5 text-sm" />
                 </div>
                 <button onClick={loadSegment} disabled={submitting || filters.length === 0} className="bg-blue-600 text-white text-xs px-5 py-2 rounded hover:bg-blue-700 disabled:opacity-50 shrink-0">
-                  {submitting ? 'Loading…' : `Load ${segType === 'reference' ? 'Reference' : 'Segment'}`}
+                  {submitting
+                    ? (editingLogId ? 'Saving…' : 'Loading…')
+                    : (editingLogId
+                        ? `Save ${segType === 'reference' ? 'Reference' : 'Segment'}`
+                        : `Load ${segType === 'reference' ? 'Reference' : 'Segment'}`)}
                 </button>
               </div>