diff --git a/backend/api_test.go b/backend/api_test.go
index 3ba6b31..dec630e 100644
--- a/backend/api_test.go
+++ b/backend/api_test.go
@@ -782,30 +782,6 @@ func TestAddAllowanceSimple(t *testing.T) {
 	history.Value(0).Object().Value("description").String().IsEqual("Added to allowance 1")
 }
 
-func TestAddAllowanceIdZero(t *testing.T) {
-	e := startServer(t)
-
-	createTestAllowance(e, "Test Allowance 1", 1000, 1)
-
-	request := map[string]interface{}{
-		"amount":      10,
-		"description": "Added to allowance 1",
-	}
-	e.POST("/user/1/allowance/0/add").WithJSON(request).Expect().Status(200)
-
-	// Verify the allowance is updated
-	allowances := e.GET("/user/1/allowance").Expect().Status(200).JSON().Array()
-	allowances.Value(0).Object().Value("id").Number().IsEqual(0)
-	allowances.Value(0).Object().Value("progress").Number().InDelta(10.0, 0.01)
-
-	// Verify the history is updated
-	history := e.GET("/user/1/history").Expect().Status(200).JSON().Array()
-	history.Length().IsEqual(1)
-	history.Value(0).Object().Value("allowance").Number().InDelta(10.0, 0.01)
-	history.Value(0).Object().Value("timestamp").String().AsDateTime().InRange(getDelta(time.Now(), 2.0))
-	history.Value(0).Object().Value("description").String().IsEqual("Added to allowance 1")
-}
-
 func TestAddAllowanceWithSpillage(t *testing.T) {
 	e := startServer(t)
 
@@ -838,6 +814,89 @@ func TestAddAllowanceWithSpillage(t *testing.T) {
 	history.Value(0).Object().Value("description").String().IsEqual("Added to allowance 1")
 }
 
+func TestAddAllowanceIdZero(t *testing.T) {
+	e := startServer(t)
+
+	createTestAllowance(e, "Test Allowance 1", 1000, 1)
+
+	request := map[string]interface{}{
+		"amount":      10,
+		"description": "Added to allowance 1",
+	}
+	e.POST("/user/1/allowance/0/add").WithJSON(request).Expect().Status(200)
+
+	// Verify the allowance is updated
+	allowances := e.GET("/user/1/allowance").Expect().Status(200).JSON().Array()
+	allowances.Value(0).Object().Value("id").Number().IsEqual(0)
+	allowances.Value(0).Object().Value("progress").Number().InDelta(10.0, 0.01)
+
+	// Verify the history is updated
+	history := e.GET("/user/1/history").Expect().Status(200).JSON().Array()
+	history.Length().IsEqual(1)
+	history.Value(0).Object().Value("allowance").Number().InDelta(10.0, 0.01)
+	history.Value(0).Object().Value("timestamp").String().AsDateTime().InRange(getDelta(time.Now(), 2.0))
+	history.Value(0).Object().Value("description").String().IsEqual("Added to allowance 1")
+}
+
+func TestSubtractAllowanceSimple(t *testing.T) {
+	e := startServer(t)
+
+	createTestAllowance(e, "Test Allowance 1", 1000, 1)
+
+	request := map[string]interface{}{
+		"amount":      10,
+		"description": "Added to allowance 1",
+	}
+	e.POST("/user/1/allowance/1/add").WithJSON(request).Expect().Status(200)
+	request["amount"] = -2.5
+	e.POST("/user/1/allowance/1/add").WithJSON(request).Expect().Status(200)
+
+	// Verify the allowance is updated
+	allowances := e.GET("/user/1/allowance").Expect().Status(200).JSON().Array()
+	allowances.Value(1).Object().Value("id").Number().IsEqual(1)
+	allowances.Value(1).Object().Value("progress").Number().InDelta(7.5, 0.01)
+
+	// Verify the history is updated
+	history := e.GET("/user/1/history").Expect().Status(200).JSON().Array()
+	history.Length().IsEqual(2)
+	history.Value(0).Object().Value("allowance").Number().InDelta(10.0, 0.01)
+	history.Value(0).Object().Value("timestamp").String().AsDateTime().InRange(getDelta(time.Now(), 2.0))
+	history.Value(0).Object().Value("description").String().IsEqual("Added to allowance 1")
+
+	history.Value(1).Object().Value("allowance").Number().InDelta(-2.5, 0.01)
+	history.Value(1).Object().Value("timestamp").String().AsDateTime().InRange(getDelta(time.Now(), 2.0))
+	history.Value(1).Object().Value("description").String().IsEqual("Added to allowance 1")
+}
+
+func TestSubtractllowanceIdZero(t *testing.T) {
+	e := startServer(t)
+
+	createTestAllowance(e, "Test Allowance 1", 1000, 1)
+
+	request := map[string]interface{}{
+		"amount":      10,
+		"description": "Added to allowance 1",
+	}
+	e.POST("/user/1/allowance/0/add").WithJSON(request).Expect().Status(200)
+	request["amount"] = -2.5
+	e.POST("/user/1/allowance/0/add").WithJSON(request).Expect().Status(200)
+
+	// Verify the allowance is updated
+	allowances := e.GET("/user/1/allowance").Expect().Status(200).JSON().Array()
+	allowances.Value(0).Object().Value("id").Number().IsEqual(0)
+	allowances.Value(0).Object().Value("progress").Number().InDelta(7.5, 0.01)
+
+	// Verify the history is updated
+	history := e.GET("/user/1/history").Expect().Status(200).JSON().Array()
+	history.Length().IsEqual(2)
+	history.Value(0).Object().Value("allowance").Number().InDelta(10.0, 0.01)
+	history.Value(0).Object().Value("timestamp").String().AsDateTime().InRange(getDelta(time.Now(), 2.0))
+	history.Value(0).Object().Value("description").String().IsEqual("Added to allowance 1")
+
+	history.Value(1).Object().Value("allowance").Number().InDelta(-2.5, 0.01)
+	history.Value(1).Object().Value("description").String().IsEqual("Added to allowance 1")
+}
+
 func getDelta(base time.Time, delta float64) (time.Time, time.Time) {
 	start := base.Add(-time.Duration(delta) * time.Second)
 	end := base.Add(time.Duration(delta) * time.Second)
diff --git a/backend/db.go b/backend/db.go
index 37d6fbb..4c0aaf3 100644
--- a/backend/db.go
+++ b/backend/db.go
@@ -562,11 +562,39 @@ func (db *Db) AddAllowanceAmount(userId int, allowanceId int, request AddAllowan
 	}
 
 	if allowanceId == 0 {
+		if remainingAmount < 0 {
+			var userBalance int
+			err = tx.Query("select balance from users where id = ?").
+				Bind(userId).ScanSingle(&userBalance)
+			if err != nil {
+				return err
+			}
+			if remainingAmount > userBalance {
+				return fmt.Errorf("cannot remove more than the current balance: %d", userBalance)
+			}
+		}
 		err = tx.Query("update users set balance = balance + ? where id = ?").
 			Bind(remainingAmount, userId).Exec()
 		if err != nil {
 			return err
 		}
+	} else if remainingAmount < 0 {
+		var progress int
+		err = tx.Query("select balance from allowances where id = ? and user_id = ?").
+			Bind(allowanceId, userId).ScanSingle(&progress)
+		if err != nil {
+			return err
+		}
+
+		if remainingAmount > progress {
+			return fmt.Errorf("cannot remove more than the current allowance balance: %d", progress)
+		}
+
+		err = tx.Query("update allowances set balance = balance + ? where id = ? and user_id = ?").
+			Bind(remainingAmount, allowanceId, userId).Exec()
+		if err != nil {
+			return err
+		}
 	} else {
 		// Fetch the target and progress of the specified allowance
 		var target, progress int