Read the original guidance here:
HMRC SDLT: SDLTM62070 – Processing: Further guidance for completing forms SDLT1, SDLT3 and SDLT4: Further guidance for question 4 SDLT1, effective date of transaction

HMRC Guidance on Question 4 of SDLT1 Forms

Question 4 appears on both the paper SDLT1 form and the online SDLT1. This question requires you to enter the effective date of the transaction. Here’s what you need to know:

How to Enter the Date

When providing the date, you must format it as dd/mm/yyyy. This means:

• If the day or month is less than 10, you should write a 0 followed by the digit.
  For example, if the date is 5th October 2023, write 05/10/2023.

Understanding Substantial Performance

Sometimes, an agreement may be considered to have reached ‘substantial performance’ before the official completion. Substantial performance can occur under the following conditions:

• The purchaser or someone associated with them has taken possession of most or all of the property as described in the contract.
• A large part of the payment for the contract has been made.
  For agreements for lease, this includes any payments besides rent.
• The initial rent payment has been made.

According to HMRC, if 90% or more of the contract has been fulfilled, this is seen as substantial. When substantial performance occurs, the effective date you must enter on the form is the earlier date when this milestone was reached. Additionally, you may need to inform HMRC once the completion has taken place.

Important Reminders

• Do not use a future date that is later than the actual date of substantial performance. This is known as post-dating and is not allowed.
• If you need further details about what constitutes substantial performance, you can refer to the guidance at SDLTM07700.

Understanding these points is key to completing your SDLT1 form accurately and in line with HMRC regulations.