How to file a CT600 with Corporation Tax partly paid
Short version. You can file a CT600 when only part of the Corporation Tax has been paid. Report the relevant amount already paid in box 595, not the amount you intend to pay later. The return still reports the full liability and calculates the remaining balance.
1. Can you file with tax still to pay?
Payment and filing have separate deadlines. A part-payment does not prevent you preparing and filing the return, but it does not extend the payment deadline. Check what remains due with HMRC and pay on time. HMRC can charge interest when payment is late.
Do not delay the return while waiting to settle the balance. Likewise, submitting the CT600 does not arrange payment or a payment plan. Start with the filing walkthrough if you need the complete process.
2. Worked examples: part paid, fully paid and overpaid
Assume an ordinary return with £3,800 Corporation Tax liability, no other tax credits and no refunds. These examples isolate the payment. More complex returns can include additional credits in the reconciliation.
| Position | Already paid (595) | Return balance |
|---|---|---|
| Part paid | £2,000.25 | £1,799.75 outstanding (600) |
| Paid in full | £3,800.00 | £0.00 outstanding (600) |
| Overpaid | £4,000.00 | £200.00 overpaid (605) |
The liability stays £3,800 in all three examples. Box 595 changes the settlement, not the profit calculation. Never enter a negative outstanding balance to represent an overpayment.
For the overpayment example, report the actual £4,000 payment. Do not cap it at £3,800 just to make the return show zero. Any repayment is handled by HMRC and depends on the company’s account position. The return’s overpaid figure is not a promise of when money will arrive.
3. Multiple payments and refunds
If you paid £1,000 and then £500.50 for the same return, the combined payment is £1,500.50. If £200 has already been refunded, the amount not repaid is £1,300.50. Reconcile the total rather than entering each instalment as if it were a different tax liability.
Use payments actually made and not already refunded. Do not include a transfer you have only scheduled. Keep pence in the payment amount. The box 595 checklist explains the exclusions and supporting records.
4. Keep different return periods separate
Suppose return 1 has a £3,000 liability and £3,500 paid, while return 2 has a £1,000 liability and no payment. With no other credits, return 1 has £500 overpaid and return 2 has £1,000 outstanding. Do not replace those two results with a single £500 outstanding entry on one return.
A payment allocation or transfer on HMRC’s account is a separate matter. Use the company’s records and HMRC statement to establish where each payment belongs. A date change in filing software does not transfer a payment at HMRC.
5. Enter tax already paid and check the balance
In SimpleCompanyTax, open step 2 and find Tax adjustments.
- Enter the Corporation Tax you have already paid in 595 Corporation Tax already paid. Exclude any amount HMRC has refunded.
- If you are filing two returns, click + 595 Corporation Tax already paid. Enter each period’s payment in the 595 Corporation Tax already paid field under Return 1 or Return 2, using the dates shown beside each heading.
- Tick the checkbox labelled: I confirm that I supplied these tax already paid figures and checked that they are correct for these returns, excluding amounts HMRC has repaid.
We calculate how much Corporation Tax remains to pay or has been overpaid. Check the payment amount, the calculated balance and the period dates in each draft return before filing.
You can start filing with SimpleCompanyTax if your company qualifies for our active micro-entity filing service.
6. Official guidance
- HMRC: boxes 595, 600 and 605
- HMRC: filing a Company Tax Return
- HMRC: paying Corporation Tax and late-payment interest
These examples are general guidance. Check the actual tax calculation and HMRC account, including any interest or other charges, before deciding how much remains to pay.