diff --git a/src/ui/app.rs b/src/ui/app.rs
index 41888e9..5c8b114 100644
--- a/src/ui/app.rs
+++ b/src/ui/app.rs
@@ -11,6 +11,7 @@ use crate::import::wizard::ImportWizard;
 use crate::model::cell::CellValue;
 use crate::model::Model;
 use crate::persistence;
+use crate::ui::grid::{compute_col_widths, compute_row_header_width, compute_visible_cols, parse_number_format};
 use crate::view::GridLayout;
 
 /// Drill-down state: frozen record snapshot + pending edits that have not
@@ -377,6 +378,137 @@ mod tests {
         assert_eq!(app.buffers.get("command").map(|s| s.as_str()), Some("q"));
     }
 
+    #[test]
+    fn col_offset_scrolls_when_cursor_moves_past_visible_columns() {
+        use crate::model::cell::{CellKey, CellValue};
+        // Create a model with 8 wide columns. Column item names are 30 chars
+        // each → column widths ~31 chars. With term_width=80, row header ~4,
+        // data area ~76 → only ~2 columns actually fit. But the rough estimate
+        // (80−30)/12 = 4 over-counts, so viewport_effects never scrolls.
+        let mut m = Model::new("T");
+        m.add_category("Row").unwrap();
+        m.add_category("Col").unwrap();
+        m.category_mut("Row").unwrap().add_item("R1");
+        for i in 0..8 {
+            let name = format!("VeryLongColumnItemName_{i:03}");
+            m.category_mut("Col").unwrap().add_item(&name);
+        }
+        // Populate a value so the model isn't empty
+        let key = CellKey::new(vec![
+            ("Row".to_string(), "R1".to_string()),
+            ("Col".to_string(), "VeryLongColumnItemName_000".to_string()),
+        ]);
+        m.set_cell(key, CellValue::Number(1.0));
+
+        let mut app = App::new(m, None);
+        app.term_width = 80;
+
+        // Press 'l' (right) 3 times to move cursor to column 3.
+        // Only ~2 columns fit in 76 chars of data area (each col ~26 chars wide),
+        // so column 3 is well off-screen. The buggy estimate (80−30)/12 = 4
+        // thinks 4 columns fit, so it won't scroll until col 4.
+        for _ in 0..3 {
+            app.handle_key(KeyEvent::new(KeyCode::Char('l'), KeyModifiers::NONE))
+                .unwrap();
+        }
+
+        assert_eq!(
+            app.model.active_view().selected.1,
+            3,
+            "cursor should be at column 3"
+        );
+        assert!(
+            app.model.active_view().col_offset > 0,
+            "col_offset should scroll when cursor moves past visible area (only ~2 cols fit \
+             in 80-char terminal with 26-char-wide columns), but col_offset is {}",
+            app.model.active_view().col_offset
+        );
+    }
+
+    #[test]
+    fn home_jumps_to_first_col() {
+        let mut app = two_col_model();
+        app.model.active_view_mut().selected = (1, 1);
+        app.handle_key(KeyEvent::new(KeyCode::Home, KeyModifiers::NONE))
+            .unwrap();
+        assert_eq!(app.model.active_view().selected, (1, 0));
+    }
+
+    #[test]
+    fn end_jumps_to_last_col() {
+        let mut app = two_col_model();
+        app.model.active_view_mut().selected = (1, 0);
+        app.handle_key(KeyEvent::new(KeyCode::End, KeyModifiers::NONE))
+            .unwrap();
+        assert_eq!(app.model.active_view().selected, (1, 1));
+    }
+
+    #[test]
+    fn page_down_scrolls_by_three_quarters_visible() {
+        let mut app = two_col_model();
+        // Add enough rows
+        for i in 0..30 {
+            app.model
+                .category_mut("Row")
+                .unwrap()
+                .add_item(&format!("R{i}"));
+        }
+        app.term_height = 28; // ~20 visible rows → delta = 15
+        app.model.active_view_mut().selected = (0, 0);
+        app.handle_key(KeyEvent::new(KeyCode::PageDown, KeyModifiers::NONE))
+            .unwrap();
+        assert_eq!(app.model.active_view().selected.1, 0, "column preserved");
+        assert!(
+            app.model.active_view().selected.0 > 0,
+            "row should advance on PageDown"
+        );
+        // 3/4 of ~20 = 15
+        assert_eq!(app.model.active_view().selected.0, 15);
+    }
+
+    #[test]
+    fn page_up_scrolls_backward() {
+        let mut app = two_col_model();
+        for i in 0..30 {
+            app.model
+                .category_mut("Row")
+                .unwrap()
+                .add_item(&format!("R{i}"));
+        }
+        app.term_height = 28;
+        app.model.active_view_mut().selected = (20, 0);
+        app.handle_key(KeyEvent::new(KeyCode::PageUp, KeyModifiers::NONE))
+            .unwrap();
+        assert_eq!(app.model.active_view().selected.0, 5);
+    }
+
+    #[test]
+    fn tab_in_edit_mode_commits_and_moves_right() {
+        let mut app = two_col_model();
+        app.model.active_view_mut().selected = (0, 0);
+        // Enter edit mode
+        app.handle_key(KeyEvent::new(KeyCode::Char('i'), KeyModifiers::NONE))
+            .unwrap();
+        assert!(matches!(app.mode, AppMode::Editing { .. }));
+        // Type a digit
+        app.handle_key(KeyEvent::new(KeyCode::Char('5'), KeyModifiers::NONE))
+            .unwrap();
+        // Press Tab — should commit, move right, re-enter edit mode
+        app.handle_key(KeyEvent::new(KeyCode::Tab, KeyModifiers::NONE))
+            .unwrap();
+        // Should be in edit mode on column 1
+        assert!(
+            matches!(app.mode, AppMode::Editing { .. }),
+            "should be in edit mode after Tab, but mode is {:?}",
+            app.mode
+        );
+        assert_eq!(
+            app.model.active_view().selected.1,
+            1,
+            "should have moved to column 1"
+        );
+    }
+
     #[test]
     fn command_mode_buffer_cleared_on_reentry() {
         use crossterm::event::KeyEvent;
diff --git a/src/ui/grid.rs b/src/ui/grid.rs
index b97a23e..a021ec6 100644
--- a/src/ui/grid.rs
+++ b/src/ui/grid.rs
@@ -71,56 +71,23 @@ impl<'a> GridWidget<'a> {
         let n_col_levels = layout.col_cats.len().max(1);
         let n_row_levels = layout.row_cats.len().max(1);
 
-        // ── Adaptive column widths ────────────────────────────────────
-        // Size each column to fit its widest content (header + cell values)
-        // plus 1 char gap. Minimum MIN_COL_WIDTH, capped at MAX_COL_WIDTH.
-        let col_widths: Vec<u16> = {
+        let mut col_widths = compute_col_widths(self.model, &layout, fmt_comma, fmt_decimals);
+        // Records mode: also measure cell text widths (needs drill_state)
+        if layout.is_records_mode() {
             let n = layout.col_count();
-            let mut widths = vec![0u16; n];
-            // Measure column header labels
-            for ci in 0..n {
-                let header = layout.col_label(ci);
-                let w = header.width() as u16;
-                if w > widths[ci] {
-                    widths[ci] = w;
-                }
-            }
-            // Measure cell content
-            if layout.is_records_mode() {
-                for ri in 0..layout.row_count() {
-                    for (ci, wref) in widths.iter_mut().enumerate().take(n) {
-                        let s = self.records_cell_text(&layout, ri, ci);
-                        let w = s.width() as u16;
-                        if w > *wref {
-                            *wref = w;
-                        }
-                    }
-                }
-            } else {
-                // Pivot mode: measure formatted cell values
-                for ri in 0..layout.row_count() {
-                    for (ci, wref) in widths.iter_mut().enumerate().take(n) {
-                        if let Some(key) = layout.cell_key(ri, ci) {
-                            let value =
-                                self.model.evaluate_aggregated(&key, &layout.none_cats);
-                            let s = format_value(value.as_ref(), fmt_comma, fmt_decimals);
-                            let w = s.width() as u16;
-                            if w > *wref {
-                                *wref = w;
-                            }
-                        }
+            for ri in 0..layout.row_count() {
+                for (ci, wref) in col_widths.iter_mut().enumerate().take(n) {
+                    let s = self.records_cell_text(&layout, ri, ci);
+                    let w = s.width() as u16;
+                    let needed = (w + 1).max(MIN_COL_WIDTH).min(MAX_COL_WIDTH);
+                    if needed > *wref {
+                        *wref = needed;
                     }
                 }
             }
-            // +1 for gap between columns
-            widths
-                .into_iter()
-                .map(|w| (w + 1).max(MIN_COL_WIDTH).min(MAX_COL_WIDTH))
-                .collect()
-        };
+        }
 
         // ── Adaptive row header widths ───────────────────────────────
-        // Measure the widest label at each row-header level.
         let data_row_items: Vec<&Vec<String>> = layout
             .row_items
             .iter()
@@ -588,6 +555,112 @@ impl<'a> Widget for GridWidget<'a> {
     }
 }
 
+/// Compute adaptive column widths for pivot mode (header labels + cell values).
+/// Header widths use the widest *individual* level label (not the joined
+/// multi-level string), matching how the grid renderer draws each level on
+/// its own row with repeat-suppression.
+pub fn compute_col_widths(model: &Model, layout: &GridLayout, fmt_comma: bool, fmt_decimals: u8) -> Vec<u16> {
+    let n = layout.col_count();
+    let mut widths = vec![0u16; n];
+    // Measure individual header level labels
+    let data_col_items: Vec<&Vec<String>> = layout
+        .col_items
+        .iter()
+        .filter_map(|e| {
+            if let AxisEntry::DataItem(v) = e {
+                Some(v)
+            } else {
+                None
+            }
+        })
+        .collect();
+    for (ci, wref) in widths.iter_mut().enumerate().take(n) {
+        if let Some(levels) = data_col_items.get(ci) {
+            let max_level_w = levels.iter().map(|s| s.width() as u16).max().unwrap_or(0);
+            if max_level_w > *wref {
+                *wref = max_level_w;
+            }
+        }
+    }
+    if !layout.is_records_mode() {
+        for ri in 0..layout.row_count() {
+            for (ci, wref) in widths.iter_mut().enumerate().take(n) {
+                if let Some(key) = layout.cell_key(ri, ci) {
+                    let value = model.evaluate_aggregated(&key, &layout.none_cats);
+                    let s = format_value(value.as_ref(), fmt_comma, fmt_decimals);
+                    let w = s.width() as u16;
+                    if w > *wref {
+                        *wref = w;
+                    }
+                }
+            }
+        }
+        // Measure total row (column sums) — totals can be wider than any single cell
+        if layout.row_count() > 0 {
+            for (ci, wref) in widths.iter_mut().enumerate().take(n) {
+                let total: f64 = (0..layout.row_count())
+                    .filter_map(|ri| layout.cell_key(ri, ci))
+                    .map(|key| model.evaluate_aggregated_f64(&key, &layout.none_cats))
+                    .sum();
+                let s = format_f64(total, fmt_comma, fmt_decimals);
+                let w = s.width() as u16;
+                if w > *wref {
+                    *wref = w;
+                }
+            }
+        }
+    }
+    widths
+        .into_iter()
+        .map(|w| (w + 1).max(MIN_COL_WIDTH).min(MAX_COL_WIDTH))
+        .collect()
+}
+
+/// Compute the total row header width from the layout's row items.
+pub fn compute_row_header_width(layout: &GridLayout) -> u16 {
+    let n_row_levels = layout.row_cats.len().max(1);
+    let data_row_items: Vec<&Vec<String>> = layout
+        .row_items
+        .iter()
+        .filter_map(|e| {
+            if let AxisEntry::DataItem(v) = e {
+                Some(v)
+            } else {
+                None
+            }
+        })
+        .collect();
+    let sub_widths: Vec<u16> = (0..n_row_levels)
+        .map(|d| {
+            let max_label = data_row_items
+                .iter()
+                .filter_map(|v| v.get(d))
+                .map(|s| s.width() as u16)
+                .max()
+                .unwrap_or(0);
+            (max_label + 1).max(MIN_ROW_HEADER_W).min(MAX_ROW_HEADER_W)
+        })
+        .collect();
+    sub_widths.iter().sum()
+}
+
+/// Count how many columns fit starting from `col_offset` given the available width.
+pub fn compute_visible_cols(col_widths: &[u16], row_header_width: u16, term_width: u16, col_offset: usize) -> usize {
+    // Account for grid border (2 chars)
+    let data_area_width = term_width.saturating_sub(2).saturating_sub(row_header_width);
+    let mut acc = 0u16;
+    let mut count = 0usize;
+    for ci in col_offset..col_widths.len() {
+        let w = col_widths[ci];
+        if acc + w > data_area_width {
+            break;
+        }
+        acc += w;
+        count += 1;
+    }
+    count.max(1)
+}
+
 fn format_value(v: Option<&CellValue>, comma: bool, decimals: u8) -> String {
     match v {
         Some(CellValue::Number(n)) => format_f64(*n, comma, decimals),