Which CT600 Boxes Do Tax Adjustments Feed Into

When you complete the Tax Computation section in TinyTax, several adjustment fields combine to produce specific CT600 box values. This guide explains exactly where each field feeds into the form.

The Adjustment Fields and Box 155

All of the adjustment fields in the Tax Computation work together to produce Box 155 (Tax-Adjusted Trading Profit):

Field	Effect on taxable profit
Accounting profit	Starting point
Depreciation add-back	Positive — increases taxable profit
Disallowable expenses	Positive — increases taxable profit
Other tax adjustments	Positive or negative
Capital allowances / AIA	Negative — reduces taxable profit

"Other tax adjustments" does not have its own dedicated CT600 box number. It is absorbed into Box 155 along with all other adjustment items. The amount will appear as a labelled line item in your Tax Computations PDF, but not as a named box on the CT600 form itself.

From Box 155 to Box 315

Once Box 155 is calculated, it flows to Box 315 as follows:

• All adjustment items above combined → Box 155 (Tax-Adjusted Trading Profit)
• Box 155 minus Box 160 (trading losses brought forward applied this period) → Box 165 (Net Trading Profits)
• Box 165 plus Box 170 (other income such as bank interest) → Box 315 (Profits Chargeable to Corporation Tax)

Common Questions

Why does "Other tax adjustments" not have its own CT600 box?

The CT600 form uses broad income and profit categories rather than itemising every possible adjustment. The individual items are captured in your Tax Computations document, which is attached to your filing and reviewed by HMRC alongside the CT600 itself.

When should I use "Other tax adjustments"?

Common uses:

• Balancing charges on asset disposals — enter as a positive value to increase taxable profit
• Any other item that affects your taxable profit but does not fit the dedicated fields for depreciation add-back, disallowable expenses, or capital allowances