From the EFL handbook, if you really want to know:
A levy amounting to 3% of the Semi Final Net Gate Receipts Before Levy shall be payable in accordance with Article 36. The balance of the net proceeds after deduction of the levy represents the ‘Net Gate Receipts’ and such Net Gate Receipts shall be divided as follows:
5.6.1 50% of the Net Gate Receipts shall be paid into the Pool Account referred to in Article 35; and
5.6.2 the remaining 50% of the Net Gate Receipts shall be aggregated, Division by Division, and each Division’s aggregated monies shall be shared equally amongst the four Clubs taking part in that Division’s Play-Off matches.
5.7 Each Home Club shall send the 3% levy and the shares of the Net Gate Receipts to be paid Into the Pool Account to The League together with a statement of the calculations thereof within ten days of the match to be aggregated by Division.