fix: Estimated earnings now accurate to two decimal places instead of float64 max precision

cmd/entries/manual.go

@@ -167,7 +167,7 @@ func ManualCmd() *cobra.Command {
 			}
 
 			if entry.HourlyRate != nil {
-				earnings := duration.Hours() * *entry.HourlyRate
+				earnings := entry.RoundedHours() * *entry.HourlyRate
 				fmt.Printf("    %s %s\n", ui.BoldInfo("Hourly Rate:"), fmt.Sprintf("$%.2f", *entry.HourlyRate))
 				fmt.Printf("    %s %s\n", ui.BoldInfo("Earnings:"), fmt.Sprintf("$%.2f", earnings))
 			}

cmd/history/stats.go

@@ -111,7 +111,7 @@ func ShowPeriodStats(entries []*storage.TimeEntry, periodName string) {
 		totalDuration += duration
 
 		if entry.HourlyRate != nil {
-			earnings := duration.Hours() * *entry.HourlyRate
+			earnings := entry.RoundedHours() * *entry.HourlyRate
 			projectEarnings[entry.ProjectName] += earnings
 			totalEarnings += earnings
 			hasAnyEarnings = true
@@ -184,7 +184,7 @@ func ShowAllTimeStats(entries []*storage.TimeEntry, db *storage.Database) {
 		totalDuration += duration
 
 		if entry.HourlyRate != nil {
-			earnings := duration.Hours() * *entry.HourlyRate
+			earnings := entry.RoundedHours() * *entry.HourlyRate
 			projectEarnings[entry.ProjectName] += earnings
 			totalEarnings += earnings
 			hasAnyEarnings = true

internal/storage/db_test.go

@@ -477,6 +477,53 @@ func TestTimeEntryIsRunning(t *testing.T) {
 	}
 }
 
+func TestTimeEntryRoundedHours(t *testing.T) {
+	tests := []struct {
+		name     string
+		entry    *TimeEntry
+		expected float64
+	}{
+		{
+			name: "1h 49m 46s rounds to 1.83 hours",
+			entry: &TimeEntry{
+				StartTime: time.Date(2024, 1, 1, 10, 0, 0, 0, time.UTC),
+				EndTime:   timePtr(time.Date(2024, 1, 1, 11, 49, 46, 0, time.UTC)),
+			},
+			expected: 1.83,
+		},
+		{
+			name: "2h 30m 0s rounds to 2.50 hours",
+			entry: &TimeEntry{
+				StartTime: time.Date(2024, 1, 1, 10, 0, 0, 0, time.UTC),
+				EndTime:   timePtr(time.Date(2024, 1, 1, 12, 30, 0, 0, time.UTC)),
+			},
+			expected: 2.50,
+		},
+		{
+			name: "0h 5m 30s rounds to 0.09 hours",
+			entry: &TimeEntry{
+				StartTime: time.Date(2024, 1, 1, 10, 0, 0, 0, time.UTC),
+				EndTime:   timePtr(time.Date(2024, 1, 1, 10, 5, 30, 0, time.UTC)),
+			},
+			expected: 0.09,
+		},
+		{
+			name: "3h 14m 56s rounds to 3.25 hours",
+			entry: &TimeEntry{
+				StartTime: time.Date(2024, 1, 1, 10, 0, 0, 0, time.UTC),
+				EndTime:   timePtr(time.Date(2024, 1, 1, 13, 14, 56, 0, time.UTC)),
+			},
+			expected: 3.25,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			assert.Equal(t, tt.expected, tt.entry.RoundedHours())
+		})
+	}
+}
+
 // Helper functions
 func floatPtr(f float64) *float64 {
 	return &f

internal/storage/models.go

@@ -1,6 +1,9 @@
 package storage
 
-import "time"
+import (
+	"math"
+	"time"
+)
 
 // TimeEntry represents a recorded period of work on a project.
 // It includes a unique identifier, the project name, the start time,
@@ -31,4 +34,16 @@ func (t *TimeEntry) Duration() time.Duration {
 // It returns true when EndTime is nil, indicating no end timestamp has been set.
 func (t *TimeEntry) IsRunning() bool {
 	return t.EndTime == nil
+}
+
+// RoundedHours returns the duration in hours rounded to 2 decimal places.
+// This rounding is used for earnings calculations to ensure transparency:
+// the displayed hours value (e.g., "1.83 hours") matches exactly what is
+// used in billing calculations.
+//
+// Future enhancement: This could be made configurable via user settings
+// to support different rounding increments (e.g., 0.1 hours for 6-minute billing,
+// or 0.25 hours for 15-minute billing).
+func (t *TimeEntry) RoundedHours() float64 {
+	return math.Round(t.Duration().Hours()*100) / 100
 }