How free cash flow to the firm and equity are calculated under ifrs ???/

FCF calculations are not an accounting method, it’s a measure of free cash generation.

Is there a same method to calculate FCFE and FCFF under IFRS and GAAP.

Yes, but the items to use for deriving them from the cash flow statement may differ in their category placement.

Say under IFRS Interest expense is part of CFF then your formula will exclude the after tax interest “interest (1-t)” , it’ll become:

FCFF = CFO - Fixed Capital Investment ( or CAPEX)

same thing goes for dividends if they are part of CFO, then you need to adjust for it.

you need to know that the reason we add back interest is because FCFF is the free cash flow that is available to ALL equity and bondholders, so you need to account for it.

for FCFE you don’t need to bother about the interest(1-t) cause you need to pay it to see what is left for the equity holders after paying the bondholders ( remember priority of claim, bondholders get paid first).