To apply for a Pag-IBIG loan using their calculator, first visit the official Pag-IBIG Fund website. There, you can find the loan calculator tool which allows you to input your desired loan amount and repayment terms. This will give you an estimate of your monthly amortisation and total payable amount. Once you have your estimates, you can proceed to prepare the necessary documents for your loan application. For detailed guidance, it’s best to consult with Pag-IBIG representatives or check their official site for specific application requirements.