diff --git a/internal/model/budget.go b/internal/model/budget.go
new file mode 100644
index 0000000..0f968e7
--- /dev/null
+++ b/internal/model/budget.go
@@ -0,0 +1,12 @@
+package model
+
+// BudgetStats holds budget tracking and forecast data.
+type BudgetStats struct {
+	PlanCeiling       float64
+	CustomBudget      *float64
+	CurrentSpend      float64
+	DailyBurnRate     float64
+	ProjectedMonthly  float64
+	DaysRemaining     int
+	BudgetUsedPercent float64
+}
diff --git a/internal/model/metrics.go b/internal/model/metrics.go
new file mode 100644
index 0000000..5b8ff58
--- /dev/null
+++ b/internal/model/metrics.go
@@ -0,0 +1,94 @@
+package model
+
+import "time"
+
+// SummaryStats holds the top-level aggregate across all sessions.
+type SummaryStats struct {
+	TotalSessions   int
+	TotalPrompts    int
+	TotalAPICalls   int
+	TotalDurationSecs int64
+	ActiveDays      int
+
+	InputTokens           int64
+	OutputTokens          int64
+	CacheCreation5mTokens int64
+	CacheCreation1hTokens int64
+	CacheReadTokens       int64
+	TotalBilledTokens     int64
+
+	EstimatedCost float64
+	ActualCost    *float64
+	CacheSavings  float64
+	CacheHitRate  float64
+
+	CostPerDay     float64
+	TokensPerDay   int64
+	SessionsPerDay float64
+	PromptsPerDay  float64
+	MinutesPerDay  float64
+}
+
+// DailyStats holds metrics for a single calendar day.
+type DailyStats struct {
+	Date            time.Time
+	Sessions        int
+	Prompts         int
+	APICalls        int
+	DurationSecs    int64
+	InputTokens     int64
+	OutputTokens    int64
+	CacheCreation5m int64
+	CacheCreation1h int64
+	CacheReadTokens int64
+	EstimatedCost   float64
+	ActualCost      *float64
+}
+
+// ModelStats holds aggregated metrics for a single model.
+type ModelStats struct {
+	Model           string
+	APICalls        int
+	InputTokens     int64
+	OutputTokens    int64
+	CacheCreation5m int64
+	CacheCreation1h int64
+	CacheReadTokens int64
+	EstimatedCost   float64
+	SharePercent    float64
+	TrendDirection  int // -1, 0, +1 vs previous period
+}
+
+// ProjectStats holds aggregated metrics for a single project.
+type ProjectStats struct {
+	Project        string
+	Sessions       int
+	Prompts        int
+	TotalTokens    int64
+	EstimatedCost  float64
+	TrendDirection int
+}
+
+// HourlyStats holds prompt/session counts for one hour of the day.
+type HourlyStats struct {
+	Hour     int
+	Prompts  int
+	Sessions int
+	Tokens   int64
+}
+
+// WeeklyStats holds metrics for one calendar week.
+type WeeklyStats struct {
+	WeekStart    time.Time
+	Sessions     int
+	Prompts      int
+	TotalTokens  int64
+	DurationSecs int64
+	EstimatedCost float64
+}
+
+// PeriodComparison holds current and previous period data for delta computation.
+type PeriodComparison struct {
+	Current  SummaryStats
+	Previous SummaryStats
+}
diff --git a/internal/model/session.go b/internal/model/session.go
new file mode 100644
index 0000000..fe079e5
--- /dev/null
+++ b/internal/model/session.go
@@ -0,0 +1,55 @@
+package model
+
+import "time"
+
+// APICall represents one deduplicated API request (final state of a message.id).
+type APICall struct {
+	MessageID             string
+	Model                 string
+	Timestamp             time.Time
+	InputTokens           int64
+	OutputTokens          int64
+	CacheCreation5mTokens int64
+	CacheCreation1hTokens int64
+	CacheReadTokens       int64
+	ServiceTier           string
+	EstimatedCost         float64
+}
+
+// ModelUsage tracks per-model token usage within a session.
+type ModelUsage struct {
+	APICalls              int
+	InputTokens           int64
+	OutputTokens          int64
+	CacheCreation5mTokens int64
+	CacheCreation1hTokens int64
+	CacheReadTokens       int64
+	EstimatedCost         float64
+}
+
+// SessionStats holds aggregated metrics for a single session file.
+type SessionStats struct {
+	SessionID     string
+	Project       string
+	ProjectPath   string
+	FilePath      string
+	IsSubagent    bool
+	ParentSession string
+	StartTime     time.Time
+	EndTime       time.Time
+	DurationSecs  int64
+
+	UserMessages int
+	APICalls     int
+
+	InputTokens           int64
+	OutputTokens          int64
+	CacheCreation5mTokens int64
+	CacheCreation1hTokens int64
+	CacheReadTokens       int64
+
+	Models map[string]*ModelUsage
+
+	EstimatedCost float64
+	CacheHitRate  float64
+}