A HCSA requires that the dollar allocation be determined at the start of the yearly term, once this is set the amount cannot be changed until the plans annual renewal. For example if you select to have $3000 allocated for your HCSA for a plan that starts on July 1st, 2024, you cannot change that amount until you renew that plan again on July 1st, 2025; one full calendar year later. Any costs outside of the predetermined $3000 would be out of pocket and not covered under your HCSA.