[sokoloff]

The threshold for finding of “unreasonable” is surprisingly lax in normal times. It’s no doubt going to be more lax now, especially if the discrepancy was remotely plausibly COVID-19 impacted (inability to use your normal preparer, access your mail, whatever).

I file the 4868 literally every year; I’ve never had any estimate even questioned, let alone overturned, despite sometimes being off by mid-high 5 figures (usually over, sometimes under).

The IRS seems content as long as you’re showing any reasonable intention to comply with your obligations. Everyone is afraid of them because of their power. That’s sensible. My experience (including two audits, one a TCMP audit) is that, while they move at government speed, they are quite reasonable and even helpful to deal with.