diff --git a/src/__tests__/constraint.test.ts b/src/__tests__/constraint.test.ts
index bce9176..833ece4 100644
--- a/src/__tests__/constraint.test.ts
+++ b/src/__tests__/constraint.test.ts
@@ -1,6 +1,22 @@
 import moment, { Moment } from "moment";
+import { map } from "ramda";
 
-import { eq, ge, gt, le, lt, ne, validate } from "../constraint";
+import {
+  eq,
+  ge,
+  gt,
+  le,
+  lt,
+  ne,
+  onFriday,
+  onMonday,
+  onSathurday,
+  onSunday,
+  onThursday,
+  onTuesday,
+  onWednesday,
+  validate,
+} from "../constraint";
 import { addInterval } from "../interval";
 
 describe("validate", () => {
@@ -64,3 +80,43 @@ describe("comparison constraints", () => {
     expect(injectCurrent(gt(less))).toBe(true);
   });
 });
+
+describe("weekday constraints", () => {
+  const daysOfTheWeek = [1, 2, 3, 4, 5, 6, 7];
+
+  const ds = map(
+    (x: number) =>
+      moment("2020-10-12 17:23:57")
+        .clone()
+        .add(x - 1, "days"),
+    daysOfTheWeek,
+  );
+
+  test("onMonday", () => {
+    ds.forEach((d) => expect(onMonday(d)).toBe(d.isoWeekday() === 1));
+  });
+
+  test("onTuesday", () => {
+    ds.forEach((d) => expect(onTuesday(d)).toBe(d.isoWeekday() === 2));
+  });
+
+  test("onWednesday", () => {
+    ds.forEach((d) => expect(onWednesday(d)).toBe(d.isoWeekday() === 3));
+  });
+
+  test("onThursday", () => {
+    ds.forEach((d) => expect(onThursday(d)).toBe(d.isoWeekday() === 4));
+  });
+
+  test("onFriday", () => {
+    ds.forEach((d) => expect(onFriday(d)).toBe(d.isoWeekday() === 5));
+  });
+
+  test("onSathurday", () => {
+    ds.forEach((d) => expect(onSathurday(d)).toBe(d.isoWeekday() === 6));
+  });
+
+  test("onSunday", () => {
+    ds.forEach((d) => expect(onSunday(d)).toBe(d.isoWeekday() === 7));
+  });
+});
diff --git a/src/constraint.ts b/src/constraint.ts
index db54a92..9fa8d58 100644
--- a/src/constraint.ts
+++ b/src/constraint.ts
@@ -24,3 +24,11 @@ export const le = (threshold: Moment) => (current: Moment): boolean =>
 
 export const lt = (threshold: Moment) => (current: Moment): boolean =>
   current.isBefore(threshold); // c < t
+
+export const onMonday = (m: Moment) => m.isoWeekday() === 1;
+export const onTuesday = (m: Moment) => m.isoWeekday() === 2;
+export const onWednesday = (m: Moment) => m.isoWeekday() === 3;
+export const onThursday = (m: Moment) => m.isoWeekday() === 4;
+export const onFriday = (m: Moment) => m.isoWeekday() === 5;
+export const onSathurday = (m: Moment) => m.isoWeekday() === 6;
+export const onSunday = (m: Moment) => m.isoWeekday() === 7;