For every £100.00 that is over the adjusted net income of £50000.00, 1% of the child benefit needs to be repaid. £5000.00 over £50000.00 is equal to 50% needing to be repaid. At £60000.00 or above, then 100% would need to be repaid.
Adjusted net income includes more than just employment income, so it is possible that your tax return is including income not used on the calculator.
Personal Allowances: adjusted net income
You can also contact our Self Assessment team so we can investigate.
Self Assessment: general enquiries