What we monitor: Corporation Tax

How PenaltyProof tracks both the CT600 filing deadline and the Corporation Tax payment deadline.

What we track

PenaltyProof derives two CT deadlines from the per-company ct_period_end setting at /manage: the CT payment due date (9 months and 1 day after period end) and the CT600 filing due date (12 months after period end).

Alert stages (paid plans)

Alerts at 90, 60, 30, 14, 7, and 0 days before each of the two deadlines, plus overdue. Thresholds follow _CT_PAYMENT_THRESHOLDS and _CT_FILING_THRESHOLDS in the codebase.

Configuration required

CT alerts only fire for companies where ct_period_end is set at /manage.

What we do not monitor

We do not track the tax liability, quarterly instalment payments for large companies, or the R&D relief claim timeline. We do not communicate with HMRC — we only alert you based on the configured period end date.

Cross-link

See /deadlines/corporation-tax-return-deadline and /deadlines/corporation-tax-late-filing-penalties-2026.

Common questions

What thresholds trigger Corporation Tax alerts?

Alerts fire at 90, 60, 30, 14, 7, and 0 days before both the CT payment due date (9 months and 1 day after period end) and the CT600 filing due date (12 months after period end).

What do I need to configure?

Set ct_period_end per company at /manage. CT alerts only fire when this date is present.

Does PenaltyProof alert on quarterly instalment payments for large companies?

No. We alert on the single CT payment deadline only. Quarterly instalment payment obligations for large companies are not monitored.

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