Actually this is the standard government's way of calculation based on value of the property and tenure. If renew for 99 years for sure very expensive, like buying another property. That is why leasehold property lose value closer to the expiry date and banks won't give loan for property less than a certain number of years left.

Just be warned as there are many who say leasehold/freehold doesn't matter. It does. Just that your children or grandchildren will inherit the problem.

A next generation problem.

That's why so many don't want to buy old leasehold properties.