| # Rolling recurrence This topic describes how to extend the life of a recurrence by making it a rolling recurrence. A recurrence has a defined start date and end date, between which the recurrence functions. If the recurrence is a rolling recurrence, you can always reuse the same recurrence definition. Whenever you roll the recurrence, the recurrence's start date and end date are moved forward a specified length of time. Example Suppose the recurrence start date is January 1, 2009 and the end date is January 1, 2011. If you roll the recurrence 51 weeks forward, the result is as follows:
| Recurrence Start Date | Recurrence End Date
Before rolling | 2009-01-01 | 2011-01-01
After rolling | 2009-12-24 | 2011-12-24
Later in this topic, this example is explained in detail. The rolling process Amount of time to shift If a recurrence is rolled, ERP LN shifts the recurrence's start date, end date, and reference date forward by a specific amount of time. The amount of time by which ERP LN shifts these dates forward is calculated according to the following formula:
    A = B * F * I
The codes in the formula are defined as follows: `A`- Amount of time shifted. `B`- Length of time specified by the Recurrence Type, such as Weekly. `F`- Frequency, which is the number of days, weeks, months, or years after which the pattern repeats itself. `I`- The value of the Roll after field, also called the Interval(s) field. Note If the recurrence type is Monthly, ERP LN ensures the recurrence start date shifts to the same date of the month. For example, if the old start date is March 30, and the recurrence shifts 3 months, the start date becomes June 30. This shift amounts to 92 days. If the old end date is September 1, the end date is also shifted 92 days, and becomes December 2. Moment of rolling The rolling process can only start if the Reference Date field in the Recurrence Details (tcccp0143s000) session is so far back in the past that the reference date does not shift to a future date. Therefore, if the recurrence is rolled at the earliest possible opportunity, the rolling process shifts the reference date to the current date. To initiate the rolling process, choose one of the following methods: Update a calendar that is based on the rolling recurrence. To update a calendar, use the Update Calendars (tcccp0226m000) session. Roll the recurrence during the generation of pattern moments: Start the Generate Pattern Moments (tcccp0295m000) session. Select pattern or a range of patterns. Select the Roll Recurrence check box. To start generating pattern moments, click Generate. Manually roll the recurrence: Start the Recurrences (tcccp0143m000) session. To start the Recurrence Details (tcccp0143s000) session, double-click a recurrence. Click Roll Recurrence. Note If People retrieves dates from a recurrence to create assignments, ERP LN does not automatically roll the recurrence. Note The rolling process shifts the reference date to the recent past or current date. If the reference date is far in the past, the rolling process is automatically repeated as often as possible without shifting the reference date to a future date. Example This example is the same as the previous example, but now more details are included. Suppose a recurrence is defined as follows: Recurrence Start Date = 2009-01-01 Recurrence End Date = 2011-01-01 Reference Date = 2009-04-01 The recurrence type is Weekly, with a frequency of 1. The Roll after field, also called the Interval(s) field, is 51. Therefore, the recurrence must shift 51 weeks. The earliest opportunity to roll the occurrence is 51 weeks after the reference date, on March 24, 2010. Suppose you roll the recurrence on March 24, 2010. The following table shows the effects.
| Recurrence Start Date | Reference Date | Recurrence End Date
Before rolling | 2009-01-01 | 2009-04-01 | 2011-01-01
After rolling | 2009-12-24 | 2010-03-24 | 2011-12-24
Related topics Overview of calendars and periods To define recurrences |