Box 440 must equal Box 430 minus Box 435

Hi there,

This is a standard CT600 validation rule. Box 440 (Corporation Tax chargeable) must equal Box 430 (Tax chargeable) minus Box 435 (Income Tax deducted from gross income).

In simple terms:

• Box 430 – The total corporation tax calculated on your profits
• Box 435 – Any income tax already deducted at source (e.g. on bank interest or other income)
• Box 440 – The net corporation tax still payable (Box 430 − Box 435)

How to fix this:

1. If your company had no income tax deducted at source, make sure Box 435 is set to £0. In that case, Box 440 should equal Box 430 exactly.
2. If income tax was deducted (e.g. on bank interest), enter the correct amount in Box 435. WeFile will then automatically calculate Box 440 for you.
3. In most cases for small companies, Box 435 is simply £0 — so Box 440 = Box 430.

WeFile handles this calculation automatically in the filing wizard. If you're still seeing this error, please double-check your Profit & Loss entries to ensure the tax figures are consistent. Feel free to reply here or raise a support ticket if you need further help!