Journal Entry to write off preliminary expenses in five equal yearly instalments beginning on 31st March, 2017:

To better understand the journal entry, let's break it down into two parts:

1. Recording the initial transaction:
When incorporation expenses were debited to preliminary expenses, it means that the company initially recorded the expenses related to the incorporation process as preliminary expenses. This is a common practice, as these expenses are considered as an investment for the company's future operations.

The journal entry for this initial transaction would be as follows:
Debit: Preliminary Expenses
Credit: Cash or Bank

2. Writing off preliminary expenses in equal yearly instalments:
The company has decided to write off these preliminary expenses over a period of five years, beginning on 31st March 2017. This means that the expenses will be gradually expensed and allocated to the respective accounting periods.

To record the write-off of preliminary expenses in equal yearly instalments, the journal entry would be as follows each year:
Debit: Preliminary Expenses
Credit: Preliminary Expenses Written Off (or Profit and Loss Account)

Explanation:
The purpose of writing off preliminary expenses in equal yearly instalments is to spread the cost of these expenses over a period of time, which matches the benefits derived from them. It also helps in ensuring a more accurate representation of the company's financial performance in each accounting period.

By debiting the preliminary expenses account, we reduce the carrying value of these expenses on the balance sheet. This reflects the reduction in the value of the company's intangible assets over time.

On the other hand, crediting the preliminary expenses written off (or the profit and loss account) recognizes the expense incurred in the current accounting period. This reduces the company's profit or increases its loss for the year.

The equal yearly instalments ensure that the preliminary expenses are allocated evenly over the five-year period, providing a systematic and consistent approach to expense recognition.

Note:
It's important to consult with an accountant or a financial professional to ensure that the journal entry is recorded accurately based on the specific accounting rules and regulations applicable to your jurisdiction.

Statement of P&L A/c Dr.
To preliminary expense A/c