The amount of money to be paid monthly for pension is high.
The monthly amount to be paid for pension is high.
毎月払う年金の額が高い
直訳すると、
The amount of money to be paid monthly for pension is high.
あるいは、
The monthly amount to be paid for pension is high.
年金は、pension, national pension, annuityです。
額、金額はamount, amount of moneyです。
金額が高いは、形容詞、highを使います。
毎月は、monthly, every monthです。
every monthを使えば、
The amount of money to be paid every month for pension is high.
となります。