When is the latest day I can file and get my refund back for 2021 Taxes?

I paid 2021 Taxes and probably overpaid by a lot.
I read that I get three years to actually file a return or else I lose the tax refund.
Is this three years from April filing date or from the October extension filing date?
In other words is it by April of 2024 or October 2024?

posted

The due date to file a 2021 tax return with a tax refund is April 15, 2025 if a tax year 2021 extension was not filed. If a 2021 extension was filed then the due date is October 15, 2025.