The cost
Let’s say you took one year away from full-time work. Your salary, as reported by your employer, was around $87,500 before your time off. To get a rough idea of how much it would cost to buy back, multiply the salary you earned before your time off by the contribution rate(s) for the period you're paying for (2025's contribution rate is 12%): $87,500 × 12% = $10,500 plus interest.