Ok, after researching, what is IRS deadline for 2017 1040 w/Refund......4.15.21 or 10.15.21?

I always thought it was 3 years from date of granted extension......here being 10.15.21.

But, seeing what's shown on IRS.gov NOW believe it should be 4.15.21.

Were talking $25k, so need to absolutely correct.....my recommendation file by 4.15.21!

See sources:

IRS:

Claim a Refund

You risk losing your refund if you don't file your return. If you are due a refund for withholding or estimated taxes, you must file your return to claim it within 3 years of the return due date. - 4.15.21

Per TurboTax:

Time matters with tax refunds

April 15, 2021 is the last day to file your original 2017 tax return to claim a refund. If you received an extension for the 2017 return then your deadline is October 15, 2021.