diff --git a/README.md b/README.md
index 154eb4d..8d8c044 100644
--- a/README.md
+++ b/README.md
@@ -194,6 +194,8 @@ $ reminders show-all --search groceries
 $ reminders show-all --list Soon --list Work
 0: Ship reminders-cli (2 days ago)
 1: Contribute to open source (in 3 hours)
+$ reminders show-all --include-completed --completed-since monday
+5: Write README
 ```
 
 `--priority` and `--list` may be repeated to match any of several values. `--list` restricts which
@@ -203,7 +205,10 @@ date without a time includes the whole local day for `--due-before` (matching th
 behavior above), while `--due-after` uses the parsed date's own start as an inclusive lower bound.
 `--overdue` is independent of, and combinable with, `--due-date`/`--include-overdue`. `--no-due-date`
 cannot be combined with `--due-date`, `--due-before`, `--due-after`, `--overdue`, or
-`--include-overdue`, since those all require a due date to compare against.
+`--include-overdue`, since those all require a due date to compare against. `--completed-since`
+accepts the same natural-language dates as `--due-date`/`--due-after`, uses an inclusive lower
+bound against each reminder's completion time, and requires `--only-completed` or
+`--include-completed`, since there's nothing to filter otherwise.
 
 #### Sort reminders
 
diff --git a/Sources/RemindersLibrary/CLI.swift b/Sources/RemindersLibrary/CLI.swift
index bdcd769..1dd4dbe 100644
--- a/Sources/RemindersLibrary/CLI.swift
+++ b/Sources/RemindersLibrary/CLI.swift
@@ -65,6 +65,9 @@ private struct ShowAll: ParsableCommand {
     @Option(help: "Only show reminders from this list; repeat to specify multiple")
     var list: [String] = []
 
+    @Option(help: "Only show completed reminders completed on or after this date")
+    var completedSince: DateComponents?
+
     @Option(
         name: .shortAndLong,
         help: "format, either of 'plain' or 'json'")
@@ -82,6 +85,10 @@ private struct ShowAll: ParsableCommand {
             throw ValidationError(
                 "Cannot combine --no-due-date with --due-date, --due-before, --due-after, --overdue, or --include-overdue")
         }
+        if self.completedSince != nil && !self.onlyCompleted && !self.includeCompleted {
+            throw ValidationError(
+                "--completed-since requires --only-completed or --include-completed")
+        }
     }
 
     func run() {
@@ -96,7 +103,7 @@ private struct ShowAll: ParsableCommand {
             dueOn: self.dueDate, includeOverdue: self.includeOverdue,
             overdue: self.overdue, dueBefore: self.dueBefore, dueAfter: self.dueAfter,
             noDueDate: self.noDueDate, priorities: self.priority, search: self.search,
-            lists: self.list,
+            lists: self.list, completedSince: self.completedSince,
             displayOptions: displayOptions, outputFormat: format, sort: sort, sortOrder: sortOrder)
     }
 }
@@ -152,6 +159,9 @@ private struct Show: ParsableCommand {
     @Option(help: "Only show reminders whose title or notes contain this text (case-insensitive)")
     var search: String?
 
+    @Option(help: "Only show completed reminders completed on or after this date")
+    var completedSince: DateComponents?
+
     @Option(
         name: .shortAndLong,
         help: "format, either of 'plain' or 'json'")
@@ -169,6 +179,10 @@ private struct Show: ParsableCommand {
             throw ValidationError(
                 "Cannot combine --no-due-date with --due-date, --due-before, --due-after, --overdue, or --include-overdue")
         }
+        if self.completedSince != nil && !self.onlyCompleted && !self.includeCompleted {
+            throw ValidationError(
+                "--completed-since requires --only-completed or --include-completed")
+        }
     }
 
     func run() {
@@ -183,6 +197,7 @@ private struct Show: ParsableCommand {
             withNameOrId: self.listNameOrId, dueOn: self.dueDate, includeOverdue: self.includeOverdue,
             overdue: self.overdue, dueBefore: self.dueBefore, dueAfter: self.dueAfter,
             noDueDate: self.noDueDate, priorities: self.priority, search: self.search,
+            completedSince: self.completedSince,
             displayOptions: displayOptions, outputFormat: format, sort: sort, sortOrder: sortOrder)
     }
 }
diff --git a/Sources/RemindersLibrary/EKReminder+Encodable.swift b/Sources/RemindersLibrary/EKReminder+Encodable.swift
index b4c7cea..0aa5ea5 100644
--- a/Sources/RemindersLibrary/EKReminder+Encodable.swift
+++ b/Sources/RemindersLibrary/EKReminder+Encodable.swift
@@ -38,7 +38,7 @@ extension EKReminder: @retroactive Encodable {
         // url field is nil
         // https://developer.apple.com/forums/thread/128140
         try container.encodeIfPresent(self.url, forKey: .url)
-        try container.encodeIfPresent(format(self.completionDate), forKey: .completionDate)
+        try container.encode(format(self.completionDate), forKey: .completionDate)
 
         for alarm in self.alarms ?? [] {
             if let location = alarm.structuredLocation {
diff --git a/Sources/RemindersLibrary/Reminders.swift b/Sources/RemindersLibrary/Reminders.swift
index d6d9127..4a330ee 100644
--- a/Sources/RemindersLibrary/Reminders.swift
+++ b/Sources/RemindersLibrary/Reminders.swift
@@ -63,9 +63,10 @@ private func format(_ reminder: EKReminder, at index: Int?, listName: String? =
 
 // Additional, independently-composable filters for `show`/`show-all`, ANDed together and ANDed
 // with the pre-existing day-granularity `--due-date`/`--include-overdue` filter. `now`,
-// `dueBefore`, and `dueAfter` are resolved to concrete `Date`s once per command invocation by
-// the caller, not per reminder. Kept internal (not private) so it's directly unit-testable via
-// `@testable import`, matching `recurrenceEndDate`/`nextOccurrence` elsewhere in this file.
+// `dueBefore`, `dueAfter`, and `completedSince` are resolved to concrete `Date`s once per command
+// invocation by the caller, not per reminder. Kept internal (not private) so it's directly
+// unit-testable via `@testable import`, matching `recurrenceEndDate`/`nextOccurrence` elsewhere in
+// this file.
 func matchesAdditionalFilters(
     _ reminder: EKReminder,
     now: Date,
@@ -74,7 +75,8 @@ func matchesAdditionalFilters(
     dueAfter: Date?,
     noDueDate: Bool,
     priorities: [Priority],
-    search: String?
+    search: String?,
+    completedSince: Date? = nil
 ) -> Bool {
     let reminderDueDate = reminder.dueDateComponents?.date
 
@@ -90,6 +92,9 @@ func matchesAdditionalFilters(
     if let dueAfter, !(reminderDueDate.map { $0 >= dueAfter } ?? false) {
         return false
     }
+    if let completedSince, !(reminder.completionDate.map { $0 >= completedSince } ?? false) {
+        return false
+    }
     if !priorities.isEmpty {
         let reminderPriority = Priority(reminder.mappedPriority) ?? .none
         if !priorities.contains(reminderPriority) {
@@ -479,7 +484,7 @@ public final class Reminders {
         dueOn dueDate: DateComponents?, includeOverdue: Bool,
         overdue: Bool = false, dueBefore: DateComponents? = nil, dueAfter: DateComponents? = nil,
         noDueDate: Bool = false, priorities: [Priority] = [], search: String? = nil,
-        lists: [String] = [],
+        lists: [String] = [], completedSince: DateComponents? = nil,
         displayOptions: DisplayOptions, outputFormat: OutputFormat, sort: Sort, sortOrder: CustomSortOrder
     ) {
         let semaphore = DispatchSemaphore(value: 0)
@@ -490,6 +495,7 @@ public final class Reminders {
         // lower bound.
         let dueBeforeDate = dueBefore.flatMap { recurrenceEndDate(from: $0) }
         let dueAfterDate = dueAfter?.date
+        let completedSinceDate = completedSince?.date
         // Resolving --list up front means an unknown list name or ID hard-errors via
         // calendar(withNameOrId:)'s existing exit(1) before any reminders are fetched.
         let calendars = lists.isEmpty ? self.getCalendars() : lists.map { self.calendar(withNameOrId: $0) }
@@ -520,7 +526,8 @@ public final class Reminders {
 
                 guard matchesAdditionalFilters(
                     reminder, now: now, overdue: overdue, dueBefore: dueBeforeDate,
-                    dueAfter: dueAfterDate, noDueDate: noDueDate, priorities: priorities, search: search
+                    dueAfter: dueAfterDate, noDueDate: noDueDate, priorities: priorities, search: search,
+                    completedSince: completedSinceDate
                 ) else {
                     continue
                 }
@@ -547,6 +554,7 @@ public final class Reminders {
         withNameOrId nameOrId: String, dueOn dueDate: DateComponents?, includeOverdue: Bool,
         overdue: Bool = false, dueBefore: DateComponents? = nil, dueAfter: DateComponents? = nil,
         noDueDate: Bool = false, priorities: [Priority] = [], search: String? = nil,
+        completedSince: DateComponents? = nil,
         displayOptions: DisplayOptions, outputFormat: OutputFormat, sort: Sort, sortOrder: CustomSortOrder)
     {
         let reminderCalendar = self.calendar(withNameOrId: nameOrId)
@@ -555,6 +563,7 @@ public final class Reminders {
         let now = Date()
         let dueBeforeDate = dueBefore.flatMap { recurrenceEndDate(from: $0) }
         let dueAfterDate = dueAfter?.date
+        let completedSinceDate = completedSince?.date
 
         self.reminders(on: [reminderCalendar], displayOptions: displayOptions) { reminders in
             var matchingReminders = [(EKReminder, Int?)]()
@@ -581,7 +590,8 @@ public final class Reminders {
 
                 guard matchesAdditionalFilters(
                     reminder, now: now, overdue: overdue, dueBefore: dueBeforeDate,
-                    dueAfter: dueAfterDate, noDueDate: noDueDate, priorities: priorities, search: search
+                    dueAfter: dueAfterDate, noDueDate: noDueDate, priorities: priorities, search: search,
+                    completedSince: completedSinceDate
                 ) else {
                     continue
                 }
diff --git a/Tests/RemindersTests/FilterTests.swift b/Tests/RemindersTests/FilterTests.swift
index 7167fd8..fcb8a21 100644
--- a/Tests/RemindersTests/FilterTests.swift
+++ b/Tests/RemindersTests/FilterTests.swift
@@ -12,7 +12,8 @@ final class FilterTests: XCTestCase {
     }
 
     private func makeReminder(
-        title: String = "Test", notes: String? = nil, due: Date? = nil, priority: Priority = .none
+        title: String = "Test", notes: String? = nil, due: Date? = nil, priority: Priority = .none,
+        completed: Date? = nil
     ) -> EKReminder {
         let reminder = EKReminder(eventStore: store)
         let calendar = EKCalendar(for: .reminder, eventStore: store)
@@ -25,6 +26,10 @@ final class FilterTests: XCTestCase {
             reminder.dueDateComponents = Calendar.current.dateComponents(
                 [.year, .month, .day, .hour, .minute, .second], from: due)
         }
+        if let completed {
+            reminder.isCompleted = true
+            reminder.completionDate = completed
+        }
         return reminder
     }
 
@@ -36,11 +41,12 @@ final class FilterTests: XCTestCase {
         dueAfter: Date? = nil,
         noDueDate: Bool = false,
         priorities: [Priority] = [],
-        search: String? = nil
+        search: String? = nil,
+        completedSince: Date? = nil
     ) -> Bool {
         matchesAdditionalFilters(
             reminder, now: now, overdue: overdue, dueBefore: dueBefore, dueAfter: dueAfter,
-            noDueDate: noDueDate, priorities: priorities, search: search)
+            noDueDate: noDueDate, priorities: priorities, search: search, completedSince: completedSince)
     }
 
     func testNoFiltersMatchesEverything() throws {
@@ -95,6 +101,23 @@ final class FilterTests: XCTestCase {
         XCTAssertFalse(matches(makeReminder(), dueAfter: cutoff))
     }
 
+    func testCompletedSinceIncludesExactBoundary() throws {
+        let cutoff = wholeSecond()
+        let reminder = makeReminder(completed: cutoff)
+        XCTAssertTrue(matches(reminder, completedSince: cutoff))
+    }
+
+    func testCompletedSinceRejectsBeforeBoundary() throws {
+        let cutoff = wholeSecond()
+        let reminder = makeReminder(completed: cutoff.addingTimeInterval(-1))
+        XCTAssertFalse(matches(reminder, completedSince: cutoff))
+    }
+
+    func testCompletedSinceRejectsIncompleteReminder() throws {
+        let cutoff = wholeSecond()
+        XCTAssertFalse(matches(makeReminder(), completedSince: cutoff))
+    }
+
     func testNoDueDateMatchesReminderWithoutDueDate() throws {
         XCTAssertTrue(matches(makeReminder(), noDueDate: true))
     }