diff --git a/API.md b/API.md
index fba55dd..0547aba 100644
--- a/API.md
+++ b/API.md
@@ -1050,11 +1050,23 @@ Use `page` query parameter to navigate: `?page=2`
 - New instance has `status: pending` and calculated `due_date`
 - Recurrence stops at `recurrence_end_date` if specified
 
-**Custom RRULE Example:**
+**Custom RRULE Patterns:**
+
+`recurrence_rule` accepts a standard RFC5545 RRULE string, evaluated via `dateutil.rrule`. Currently supported: `FREQ=WEEKLY` (with `INTERVAL` and `BYDAY`) and `FREQ=MONTHLY` (with `INTERVAL` and either `BYMONTHDAY` or an ordinal-prefixed `BYDAY`). The web UI's Custom recurrence builder generates these same strings.
+
+| Pattern | `recurrence_rule` |
+|---|---|
+| Every Wednesday | `FREQ=WEEKLY;INTERVAL=1;BYDAY=WE` |
+| Every other Wednesday | `FREQ=WEEKLY;INTERVAL=2;BYDAY=WE` |
+| Every Mon/Wed/Fri | `FREQ=WEEKLY;INTERVAL=1;BYDAY=MO,WE,FR` |
+| Every 15th of the month | `FREQ=MONTHLY;INTERVAL=1;BYMONTHDAY=15` |
+| Every second Tuesday | `FREQ=MONTHLY;INTERVAL=1;BYDAY=2TU` |
+| Last Friday of the month | `FREQ=MONTHLY;INTERVAL=1;BYDAY=-1FR` |
+
 ```json
 {
   "recurrence": "custom",
-  "recurrence_rule": "FREQ=WEEKLY;BYDAY=MO,WE,FR",
+  "recurrence_rule": "FREQ=MONTHLY;INTERVAL=1;BYDAY=2TU",
   "recurrence_end_date": "2024-12-31"
 }
 ```
diff --git a/CLAUDE.md b/CLAUDE.md
index 2860536..5f58de6 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -97,7 +97,7 @@ celery -A config beat -l info
 **tasks/** - Core task management
 - Hierarchical tasks with parent/subtask relationships
 - Task status (pending, in_progress, completed, cancelled) and priority (low, medium, high, urgent)
-- Recurrence patterns (daily, weekly, monthly, yearly, custom RRULE)
+- Recurrence patterns (daily, weekly, biweekly, monthly, yearly, or custom RRULE for day-of-week/nth-weekday/day-of-month control)
 - Time tracking with start/stop timer functionality
 - Tag system with colors and icons for organization
 - Task sharing with permission levels (viewer/editor)
@@ -234,7 +234,7 @@ Configured in `config/celery.py`:
 - Hierarchy: `parent` (ForeignKey to self)
 - Status: pending, in_progress, completed, cancelled
 - Priority: low, medium, high, urgent
-- Recurrence: `recurrence_type`, `recurrence_interval`, `recurrence_rule` (RRULE)
+- Recurrence: `recurrence` (none/daily/weekly/biweekly/monthly/yearly/custom), `recurrence_rule` (RRULE string, used when `recurrence='custom'`, parsed via `dateutil.rrule`), `recurrence_end_date`
 - Timing: `due_date`, `due_time`, `completed_at`, `created_at`, `updated_at`
 - Soft delete: `is_deleted` (filters via `SoftDeleteManager`)
 - Sync: `sync_id` (UUID for mobile sync)
@@ -362,7 +362,7 @@ make test                            # Run tests in container
 
 ### Common Development Patterns
 
-**Creating Recurring Tasks:** When a recurring task is marked complete, the next recurrence is automatically created in `tasks/models.py` `create_next_recurrence()` method. Celery task `process_recurring_tasks()` runs as safety net.
+**Creating Recurring Tasks:** When a recurring task is marked complete, the next recurrence is automatically created in `tasks/models.py` `create_next_recurrence()` method, which calls `calculate_next_due_date()`. For `recurrence='custom'`, the next date is computed by evaluating `recurrence_rule` (an RRULE string) via `dateutil.rrule`; the web UI's Custom recurrence builder (in `templates/tasks/_recurrence_fields.html` and `static/js/app.js`) generates these strings for day-of-week, nth-weekday, and day-of-month patterns. Celery task `process_recurring_tasks()` runs as safety net.
 
 **Time Entry Workflow:**
 1. `POST /api/tasks/<id>/start-timer/` creates TimeEntry with start_time
diff --git a/README.md b/README.md
index b334d56..36cf610 100644
--- a/README.md
+++ b/README.md
@@ -9,7 +9,7 @@ A powerful Django-based task management system with time tracking, tag organizat
 - **Priority Levels**: Low, Medium, High, and Urgent
 - **Status Tracking**: Pending, In Progress, Completed, Cancelled
 - **Due Dates & Times**: Set specific due dates and times for tasks
-- **Recurrence**: Daily, Weekly, Bi-weekly, Monthly, Yearly, and Custom patterns
+- **Recurrence**: Daily, Weekly, Bi-weekly, Monthly, Yearly, plus Custom RRULE patterns (e.g. every other Wednesday, every second Tuesday, every 15th of the month)
 
 ### Organization
 - **Tag-Based System**: Organize tasks with multiple colored tags