diff --git a/src/ClaudeDo.Worker/Usage/TokenTracker/TokenTrackerAggregator.cs b/src/ClaudeDo.Worker/Usage/TokenTracker/TokenTrackerAggregator.cs
new file mode 100644
index 00000000..9b3308b1
--- /dev/null
+++ b/src/ClaudeDo.Worker/Usage/TokenTracker/TokenTrackerAggregator.cs
@@ -0,0 +1,105 @@
+namespace ClaudeDo.Worker.Usage.TokenTracker;
+
+public sealed record TokenTrackerTotals(long TotalTokens, double CostUsd, int Sessions);
+
+/// <summary>
+/// Pure aggregation over a parsed export. One fetch covers the whole history — <c>--from</c> and
+/// <c>--to</c> are accepted by the CLI but do <b>not</b> filter its output (measured against
+/// v0.88.4: identical 886 rows with and without a range) — so filtering here is load-bearing, and
+/// switching the range in the UI costs nothing.
+/// </summary>
+public static class TokenTrackerAggregator
+{
+    public const string ScopeClaudeDo = "claudedo";
+    public const string ScopeOther = "other";
+
+    public static IReadOnlyList<TokenTrackerModelRow> ByModel(
+        IReadOnlyList<TokenTrackerSession> sessions,
+        DateOnly from,
+        DateOnly to,
+        ISet<string> claudeDoHashes)
+    {
+        var buckets = new Dictionary<(DateOnly Date, string Model, string Scope), Accumulator>();
+
+        foreach (var session in InRange(sessions, from, to))
+        {
+            var key = (
+                DateOf(session),
+                session.Model,
+                claudeDoHashes.Contains(session.SessionHash) ? ScopeClaudeDo : ScopeOther);
+
+            if (!buckets.TryGetValue(key, out var acc))
+            {
+                acc = new Accumulator();
+                buckets[key] = acc;
+            }
+
+            acc.Input += session.InputTokens;
+            acc.Output += session.OutputTokens;
+            acc.CacheRead += session.CacheReadTokens;
+            acc.CacheCreation += session.CacheCreationTokens;
+            acc.Cost += session.CostUsd;
+            acc.Sessions++;
+        }
+
+        return buckets
+            .Select(kv => new TokenTrackerModelRow(
+                kv.Key.Date, kv.Key.Model, kv.Key.Scope,
+                kv.Value.Input, kv.Value.Output, kv.Value.CacheRead, kv.Value.CacheCreation,
+                kv.Value.Sessions, kv.Value.Cost))
+            .OrderBy(r => r.Date).ThenBy(r => r.Model).ThenBy(r => r.Scope)
+            .ToList();
+    }
+
+    /// <summary>Cost and efficiency for one task, given the session ids of its runs. Null when
+    /// none of them appear in the export — the caller then shows tokens without cost. Several
+    /// export rows can share one session hash (they are disjoint segments of the same session),
+    /// so summing every match is correct rather than double-counting.</summary>
+    public static TokenTrackerTaskExtras? ForSessions(
+        IReadOnlyList<TokenTrackerSession> sessions,
+        IEnumerable<string?> sessionIds)
+    {
+        var wanted = sessionIds
+            .Select(SessionHash.ForClaudeSession)
+            .Where(h => h is not null)
+            .ToHashSet()!;
+
+        if (wanted.Count == 0) return null;
+
+        var matched = sessions.Where(s => wanted.Contains(s.SessionHash)).ToList();
+        if (matched.Count == 0) return null;
+
+        return new TokenTrackerTaskExtras(
+            CostUsd: matched.Sum(s => s.CostUsd),
+            Retries: matched.Sum(s => s.RetryTurns),
+            Productive: matched.Any(s => s.Productive),
+            OneShot: matched.All(s => s.OneShot));
+    }
+
+    public static TokenTrackerTotals Totals(
+        IReadOnlyList<TokenTrackerSession> sessions, DateOnly from, DateOnly to)
+    {
+        var inRange = InRange(sessions, from, to).ToList();
+        return new TokenTrackerTotals(
+            TotalTokens: inRange.Sum(s =>
+                s.InputTokens + s.OutputTokens + s.CacheReadTokens + s.CacheCreationTokens),
+            CostUsd: inRange.Sum(s => s.CostUsd),
+            Sessions: inRange.Count);
+    }
+
+    private static IEnumerable<TokenTrackerSession> InRange(
+        IReadOnlyList<TokenTrackerSession> sessions, DateOnly from, DateOnly to) =>
+        sessions.Where(s => DateOf(s) >= from && DateOf(s) <= to);
+
+    /// <summary>Local start date — the UI's pickers and the old transcript reader both work in
+    /// local time, so a UTC-based date would shift rows across midnight for the user.</summary>
+    private static DateOnly DateOf(TokenTrackerSession session) =>
+        DateOnly.FromDateTime(session.StartedAt.LocalDateTime);
+
+    private sealed class Accumulator
+    {
+        public long Input, Output, CacheRead, CacheCreation;
+        public double Cost;
+        public int Sessions;
+    }
+}
diff --git a/tests/ClaudeDo.Worker.Tests/Usage/TokenTracker/TokenTrackerAggregatorTests.cs b/tests/ClaudeDo.Worker.Tests/Usage/TokenTracker/TokenTrackerAggregatorTests.cs
new file mode 100644
index 00000000..ffebe5ac
--- /dev/null
+++ b/tests/ClaudeDo.Worker.Tests/Usage/TokenTracker/TokenTrackerAggregatorTests.cs
@@ -0,0 +1,106 @@
+using ClaudeDo.Worker.Usage.TokenTracker;
+
+namespace ClaudeDo.Worker.Tests.Usage.TokenTracker;
+
+public sealed class TokenTrackerAggregatorTests
+{
+    private static readonly DateOnly RangeStart = new(2026, 8, 20);
+    private static readonly DateOnly RangeEnd = new(2026, 8, 21);
+
+    private static IReadOnlyList<TokenTrackerSession> Sessions() =>
+        TokenTrackerExportParser.Parse(
+            TokenTrackerFixtures.SessionsJson,
+            new DateTime(2026, 8, 24, 9, 0, 0, DateTimeKind.Utc))!.Sessions;
+
+    private static HashSet<string> ClaudeDoHashes() =>
+    [
+        SessionHash.ForClaudeSession(TokenTrackerFixtures.ClaudeDoSessionIdA)!,
+        SessionHash.ForClaudeSession(TokenTrackerFixtures.ClaudeDoSessionIdB)!,
+    ];
+
+    [Fact]
+    public void ByModel_ExcludesSessionsOutsideTheRange()
+    {
+        var rows = TokenTrackerAggregator.ByModel(Sessions(), RangeStart, RangeEnd, ClaudeDoHashes());
+
+        Assert.All(rows, r => Assert.InRange(r.Date, RangeStart, RangeEnd));
+        Assert.DoesNotContain(rows, r => r.CostUsd == 99.0);
+    }
+
+    [Fact]
+    public void ByModel_SplitsClaudeDoFromOther()
+    {
+        var rows = TokenTrackerAggregator.ByModel(Sessions(), RangeStart, RangeEnd, ClaudeDoHashes());
+
+        var opus = rows.Single(r => r.Model == "claude-opus-5" && r.Scope == "claudedo");
+        Assert.Equal(110, opus.InputTokens);
+        Assert.Equal(440, opus.OutputTokens);
+        Assert.Equal(990, opus.CacheReadTokens);
+        Assert.Equal(55, opus.CacheCreationTokens);
+        Assert.Equal(2, opus.Sessions);
+        Assert.Equal(3.5, opus.CostUsd, 6);
+
+        var sonnet = rows.Single(r => r.Model == "claude-sonnet-5");
+        Assert.Equal("other", sonnet.Scope);
+        Assert.Equal(0.25, sonnet.CostUsd, 6);
+    }
+
+    [Fact]
+    public void ByModel_UnknownHash_CountsAsOther()
+    {
+        var rows = TokenTrackerAggregator.ByModel(Sessions(), RangeStart, RangeEnd, new HashSet<string>());
+
+        Assert.All(rows, r => Assert.Equal("other", r.Scope));
+    }
+
+    [Fact]
+    public void ByModel_EmptyInput_ReturnsEmpty()
+    {
+        Assert.Empty(TokenTrackerAggregator.ByModel([], RangeStart, RangeEnd, new HashSet<string>()));
+    }
+
+    [Fact]
+    public void ForSessions_SumsCostAndRetriesOfMatchingRows()
+    {
+        var extras = TokenTrackerAggregator.ForSessions(
+            Sessions(),
+            [TokenTrackerFixtures.ClaudeDoSessionIdA, TokenTrackerFixtures.ClaudeDoSessionIdB]);
+
+        Assert.NotNull(extras);
+        Assert.Equal(3.5, extras!.CostUsd, 6);
+        Assert.Equal(3, extras.Retries);
+        Assert.True(extras.Productive);   // A is productive
+        Assert.False(extras.OneShot);     // B is not one-shot
+    }
+
+    [Fact]
+    public void ForSessions_SingleOneShotSession_ReportsOneShot()
+    {
+        var extras = TokenTrackerAggregator.ForSessions(
+            Sessions(), [TokenTrackerFixtures.ClaudeDoSessionIdA]);
+
+        Assert.True(extras!.OneShot);
+        Assert.Equal(2.5, extras.CostUsd, 6);
+    }
+
+    [Fact]
+    public void ForSessions_NoMatch_ReturnsNull()
+    {
+        Assert.Null(TokenTrackerAggregator.ForSessions(Sessions(), ["11111111-2222-3333-4444-555555555555"]));
+    }
+
+    [Fact]
+    public void ForSessions_BlankIds_ReturnsNull()
+    {
+        Assert.Null(TokenTrackerAggregator.ForSessions(Sessions(), [null, "", "  "]));
+    }
+
+    [Fact]
+    public void Totals_SumsTokensAndCostInRange()
+    {
+        var totals = TokenTrackerAggregator.Totals(Sessions(), RangeStart, RangeEnd);
+
+        Assert.Equal(1615, totals.TotalTokens);   // 1450 + 145 + 20
+        Assert.Equal(3.75, totals.CostUsd, 6);
+    }
+}