Diagnostic text ONLY. Do not use this field for troubleshooting or questions. Please enter the diagnostic exactly as seen in the program. Comment AFTER posting. ***Please Delete this and the above text before posting*** The following diagnostic is generating:

The corporation's history of California taxable income categorizes it as a "large corporation." as a result, only the first estimated tax payment for 2026 can be based on 2025 income. If the corporation's California taxable income increases in 2026, the second, third and fourth estimated tax payment should be increased to avoid 2026 underpayment penalty.

Solution:  

Installments 2 and 4 must reflect the actual expected 2026 liability, not the prior-year tax.

Recommended Method

Prepare quarterly forecast updates: