State Health Care Premium Reduction Act of 2021 This bill establishes and provides funding for the Improve Health Insurance Affordability Fund. States must use allocated funds to (1) issue reinsurance payments to health insurers (i.e., reimbursements to protect insurers against exceedingly high claims) for individual health insurance coverage, or (2) provide other assistance to reduce out-of-pocket costs (e.g., copayments, coinsurance, and deductibles) for qualified health plans offered in the individual market through an exchange. Reinsurance payments using such funds may not be applied to (1) grandfathered health plans in place on March 23, 2010, (2) non-grandfathered transitional plans meeting specified requirements identified by the Centers for Medicare & Medicaid Services (CMS), or (3) student health insurance plans provided by institutions of higher education. The bill appropriates $10 billion per year for the fund, which the CMS must distribute to states in accordance with a specified methodology based on the estimated amount of reinsurance payments for individuals in a state during the given year, subject to specified deductions. Additionally, states must submit applications explaining how they will use such funds. In the event that a state does not submit an application, the bill directs the CMS to allocate the calculated funding amount to reinsurance programs in that state.