When my son was small he got .50 per year in age

Chores were expected of him as a member of the family and I paid for most extra things as we went along.

When my son reached middle school age we started looking at what we spent on him a month for his activities, sport fees, dues etc.. THings paid out once a year were divided by 12. That became his montly allowance with the expectation that he would manage the money and pay for these things himself. Extra money could be earned by doing extra chores that were not part of his normal routine. This was his to spend on as he wanted. If he over spent on a weekend, there was no money for baseball sign ups and there was no bail out from mom and dad. Hard lessons learned at an early age.

When he reached high school we added in the amount we felt was fair for clothing for the year and again divided that by 12. Allowance was paid in sync with our pay cycle at the time. So he learned to manged things monthly and bi-weekly.