diff --git a/ui/src/views/Forecast.jsx b/ui/src/views/Forecast.jsx
index 977294b..4238363 100644
--- a/ui/src/views/Forecast.jsx
+++ b/ui/src/views/Forecast.jsx
@@ -676,7 +676,7 @@ export default function Forecast({ sources = [], sourceId, versions = [], versio
         // restore() has already applied group_by_depth; this only syncs the
         // toolbar. expand_depth is the legacy key, from when depth was imperative
         // and had to be stored beside the config rather than in it.
-        if (cfg.group_by_depth != null) setExpandDepth(cfg.group_by_depth)
+        if (cfg.group_by_depth != null) setExpandDepth(cfg.group_by_depth - 1)
         else if (cfg.expand_depth != null) await applyDepth(cfg.expand_depth)
       } else {
         const sourceDefault = sources.find(s => String(s.id) === String(sid))?.default_layout
@@ -832,11 +832,18 @@ export default function Forecast({ sources = [], sourceId, versions = [], versio
   async function applyDepth(d) {
     const viewer = viewerRef.current
     if (!viewer) return
-    // A partial restore({ group_by_depth }) on its own did nothing, so the whole
-    // config goes back with the field changed. table is dropped: it is loaded by
-    // reference, and a stale name in the config fails the lookup.
+    // group_by_depth counts levels, where view.set_depth() counts the boundary
+    // below them -- server.cpp does ctx->set_depth(row_pivot_depth - 1) for both
+    // the one- and two-sided contexts. So the toolbar's 0..3, which were written
+    // against the imperative call, are one less than the config wants: depth 0
+    // (grand total only) is group_by_depth 1, and passing 0 asked the engine for
+    // set_depth(-1).
+    //
+    // The whole config goes back rather than a partial update, which had no
+    // effect on its own. table is dropped: it is loaded by reference, and a stale
+    // name in a restored config fails the lookup.
     const { table: _t, ...cfg } = await viewer.save()
-    await viewer.restore({ ...cfg, group_by_depth: d })
+    await viewer.restore({ ...cfg, group_by_depth: d + 1 })
     setExpandDepth(d)
   }
 
@@ -906,7 +913,7 @@ export default function Forecast({ sources = [], sourceId, versions = [], versio
     cfg.plugin_config = { ...(cfg.plugin_config || {}), edit_mode: 'SELECT_REGION' }
     await viewer.restore(cfg)
     adoptSplit(cfg.split_full?.length ? cfg.split_full : cfg.split_by, (cfg.split_by || []).length)
-    if (cfg.group_by_depth != null) setExpandDepth(cfg.group_by_depth)
+    if (cfg.group_by_depth != null) setExpandDepth(cfg.group_by_depth - 1)
     else if (cfg.expand_depth != null) await applyDepth(cfg.expand_depth)
     setActiveLayoutId(layout.id)
     await persistLayout(versionId, cfg)