Property LtdCos sit inside the Corporation Tax Self-Assessment (CTSA) cycle, which has two distinct deadlines and a layered penalty architecture that differs materially from the personal self-assessment regime that individual landlords are used to. The CT600 return is due 12 months after the end of the accounting period under Schedule 18 paragraph 14 of the Finance Act 1998. The Corporation Tax itself is due earlier: 9 months and 1 day after the end of the accounting period for small companies under TMA 1970 section 59D, or in four quarterly instalments for large and very-large companies under SI 1998/3175.

The deadlines look simple on first reading. The complexity comes from the associated-companies divisor that pulls multi-SPV portfolio operators into the quarterly-instalment regime at much lower per-SPV profit levels than the headline £1.5m threshold suggests, the CIHC (close investment-holding company) overlay that denies the small profits rate to companies failing the section 18N qualifying-purpose carve-out, and the Schedule 18 paragraph 17 flat-rate penalty figures that were re-verified in May 2026 at £200 / £400 / £1,000 / £2,000 against legacy £100 / £200 / £500 / £1,000 figures still carried in older guides.

This page is the property-LtdCo deadline-and-penalty architecture. We cover both deadlines, the instalment regime, the associated-companies divisor, the late-filing penalty schedule, the Schedule 56 late-payment escalator, the Schedule 24 inaccuracy interaction, the record-retention obligation under Companies Act 2006 section 388, and the property-specific scenarios that trip up landlord SPV operators most often.

The CT600 filing deadline: 12 months after end of accounting period

Schedule 18 paragraph 14 of the Finance Act 1998 sets the filing date for a company tax return as the last day of whichever of the following periods is last to end:

  • 12 months from the end of the period for which the return is made;
  • If the company delivers accounts under section 441 of the Companies Act 2006 later than that 12-month point, 3 months from the date of delivery of those accounts;
  • 3 months from the date HMRC served a notice requiring the return where notice was served after the 12-month standard date;
  • For new companies, 3 months from when the notice was served where that is later than the 12-month standard.

For most landlord LtdCos with timely accounts and a HMRC notice already in place, the operational deadline is the 12-month rule. For a 31 March 2026 year-end, the CT600 is due 31 March 2027. A short first accounting period for a newly-incorporated SPV shifts the deadline: an SPV incorporated 1 November 2025 with a first ARD of 30 November 2026 has a first CT600 due 30 November 2027 covering the short 1 November 2025 to 30 November 2026 AP.

The CT payment deadline: 9 months and 1 day for small companies

TMA 1970 section 59D (read with CTA 2010 section 6) sets the Corporation Tax due date for companies not within the quarterly-instalment regime at 9 months and 1 day after the end of the accounting period. For a 31 March 2026 year-end, CT is due 1 January 2027.

The payment deadline runs 3 months ahead of the filing deadline in the standard cycle. The operational consequence is that small-company directors must estimate and pay the CT before the CT600 is finalised. The standard sequence is:

  1. 9 months 1 day after AP end: CT payment due. Director pays the estimated liability based on draft accounts.
  2. Up to 3 months later: CT600 finalised and filed. If the actual liability differs from the estimated payment, the difference is settled (HMRC issues interest on under-payment, refund or credit on over-payment).
  3. 12 months after AP end: CT600 filing deadline.

A small-company SPV that delays both payment and filing to the filing deadline (12 months after AP end) is, in effect, 3 months late on the payment and exposed to the Schedule 56 escalator on the unpaid CT.

Quarterly instalment payments for large and very-large companies

Companies with augmented profits above £1.5 million in the accounting period pay CT in four quarterly instalments under the Corporation Tax (Instalment Payments) Regulations 1998 (SI 1998/3175). The instalments fall at months 7, 10, 13, and 16 from the start of the accounting period. Each instalment is one quarter of the estimated full-year CT liability. The instalments run on a 4-payment schedule that straddles the accounting period itself: by the time the last instalment falls due, the AP has ended and the year is closed.

Very-large companies (augmented profits above £20 million) accelerate to instalments at months 3, 6, 9, and 12 from the start of the accounting period under SI 1998/3175 as amended by FA 2017. The very-large regime brings the full CT liability inside the AP itself: the last instalment falls due in the last month of the AP.

Augmented profits is defined for these purposes as the company's taxable total profits plus exempt distributions from non-group companies. The threshold testing is annual and is performed at the start of each AP based on the company's expected profit position.

The associated-companies divisor: the most-missed CT mechanic

Both the £1.5 million and £20 million instalment thresholds are divided by 1 plus the number of associated companies under CTA 2010 section 18E. The same divisor applies to the £50,000 lower band and the £250,000 upper band of the small profits rate / marginal relief framework under section 18N.

For a multi-SPV property operator with 4 associated companies (5 companies in total including the SPV being tested), the divisor is 5 and the thresholds become:

  • Instalment-threshold (large): £1,500,000 ÷ 5 = £300,000
  • Instalment-threshold (very-large): £20,000,000 ÷ 5 = £4,000,000
  • Small profits rate upper band: £50,000 ÷ 5 = £10,000
  • Marginal relief upper band: £250,000 ÷ 5 = £50,000

A multi-SPV operator with combined £6 million profit across the group (£1.2 million per SPV) is below the headline £1.5 million threshold but above the £300,000 per-SPV effective threshold after the divisor. Each SPV must pay CT in quarterly instalments. The same operator's CT effective rate on the per-SPV £1.2 million profit is 25% (well above the marginal-relief upper band after the divisor), so the small-profits-rate benefit is also lost.

The associated-companies definition under section 18E is broad: companies under common control (the same person or group of persons), companies linked through certain holding-company relationships, and some dormant-company scenarios. Multi-SPV property structures typically meet the common-control test on the founder shareholder. The divisor is the central reason why portfolio LtdCo structures lose more CT to instalment timing and main-rate exposure than single-SPV equivalents.

The flat-rate late-filing penalty under Schedule 18 paragraph 17

Schedule 18 paragraph 17 of FA 1998 sets the flat-rate late-filing penalty. The figures, verified live against legislation.gov.uk in May 2026, are:

First and second successive failures (paragraph 17(2))

  • £200 if the CT600 is delivered within 3 months after the filing date.
  • £400 in any other case.

Third successive failure (paragraph 17(3))

  • £1,000 if the CT600 is delivered within 3 months after the filing date.
  • £2,000 in any other case.

The third-successive trigger requires three consecutive accounting periods where the company has been in charge to Corporation Tax, has been required to deliver a return for each, and has incurred a paragraph 17 penalty for the first two. The trigger does not catch a company that has merely failed to file once before; it requires sustained failure across three APs.

These figures differ from the £100 / £200 / £500 / £1,000 figures still carried in some older accountancy-firm guides and HMRC summary pages. The legislation has been at £200 / £400 / £1,000 / £2,000 for some years; the legacy figures have been a recurring drift pattern in published commentary. Any commentary citing the lower numbers should be treated with suspicion and the verbatim current figures verified against legislation.gov.uk.

The tax-geared late-filing penalty under Schedule 18 paragraph 18

Schedule 18 paragraph 18 stacks a tax-geared penalty on top of the paragraph 17 flat-rate for returns that are significantly late:

  • 10% of unpaid CT where the return is more than 18 months late.
  • 20% of unpaid CT where the return is more than 24 months late.

The tax-geared penalty operates on the unpaid CT at the relevant due date, not at the filing date. For a £36,000 CT liability filed 24 months late, the combined Schedule 18 late-filing penalty is £400 (paragraph 17) plus £7,200 (paragraph 18 at 20%) = £7,600. The Schedule 56 late-payment escalator also stacks on the same unpaid CT (see below), and the total penalty cost of sustained late filing can quickly exceed the underlying CT liability.

The Schedule 56 late-payment escalator (item 5)

Schedule 56 FA 2009 Table item 5 applies the standard escalator architecture to Corporation Tax. The penalty cycle:

  • 5% of unpaid tax at the penalty date (typically 30 days after the due date).
  • Further 5% at 6 months after the due date.
  • Further 5% at 12 months after the due date.

Interest under FA 2009 section 101 accrues continuously alongside the penalty layer. Interest is not penalty in statutory terms but it stacks economically. For a £36,000 CT liability left unpaid for 12 months past the due date, the Schedule 56 cumulative penalty is 15% × £36,000 = £5,400, plus interest at the prevailing HMRC rate accrued daily over the 12-month period.

The Schedule 56 penalty layer is independent of the Schedule 18 late-filing penalty layer. A company that files the CT600 on time but pays the underlying CT late attracts only the Schedule 56 layer. A company that files late and also pays late attracts both layers stacking on the same unpaid CT.

Worked example 1: single-SPV normal-cycle CT timeline

Marwood Properties Ltd is a single BTL SPV with no associated companies and a 31 March year-end. The accounting period ending 31 March 2026:

  • CT600 filing date: 31 March 2027 (12 months from end of AP per Schedule 18 paragraph 14).
  • CT payment date: 1 January 2027 (9 months 1 day after end of AP per section 59D).
  • Augmented profits: £80,000 (well below £1.5m instalment threshold; single-company position so divisor is 1).
  • CT calculation: small profits rate 19% applies on the first £50,000; marginal relief on the next £30,000; CT liability around £15,200.

Operational sequence: Marwood's director pays the estimated CT on 1 January 2027 from draft management accounts. The CT600 is finalised and filed by 31 March 2027. If the actual liability differs from the estimated payment by more than a few hundred pounds, the difference is settled with interest on under-payment (FA 2009 section 101) or refund on over-payment.

Missing the 1 January 2027 payment triggers the Schedule 56 escalator from 31 January 2027 (5% at day 31). Missing the 31 March 2027 filing date triggers Schedule 18 paragraph 17 flat-rate (£200 if filed by 30 June 2027, £400 thereafter).

Worked example 2: multi-SPV portfolio pushed into instalments

Heatherden Group owns 5 SPVs (Heatherden Property 1 to 5 Ltd) under a common parent. Combined augmented profits across the group: £6 million per year, £1.2 million per SPV. Without the associated-companies divisor, each SPV's £1.2 million sits below the £1.5 million instalment threshold and would not require instalments.

With the associated-companies divisor (5 companies, divisor = 5), the £1.5 million threshold becomes £300,000 per SPV. Each SPV exceeds the threshold and must pay CT in quarterly instalments under SI 1998/3175. For a 31 March year-end SPV, instalments fall at:

  • 14 October Year 1 (month 7 from start of AP)
  • 14 January Year 2 (month 10)
  • 14 April Year 2 (month 13)
  • 14 July Year 2 (month 16)

Each instalment is one quarter of the estimated full-year CT liability for that SPV. The first two instalments fall inside the AP itself (months 7 and 10 of a 12-month AP); the second two fall after the AP has ended. The estimation discipline is high: under-payment triggers interest charges under FA 2009 section 101; over-payment is refunded but takes operational time to reclaim.

The strategic point for Heatherden's directors is that the instalment-threshold trap was not visible at the headline £1.5m level. Group structures with 4 or more associated companies should test the instalment position from the start of each AP, not at the end.

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Worked example 3: late-filing penalty progression at 3 / 6 / 18 / 24 months

Stoneleigh Investments Ltd is a single SPV with no associates. CT600 due 31 March 2027 for AP ending 31 March 2026. Augmented profits £150,000; CT liability £36,000 after marginal relief.

Scenario A: filed 30 June 2027 (3 months late). Schedule 18 paragraph 17(2)(a) flat-rate £200 (within 3 months of filing date). No tax-geared penalty. Total Schedule 18 penalty: £200.

Scenario B: filed 30 September 2027 (6 months late). Schedule 18 paragraph 17(2)(b) flat-rate £400. No tax-geared penalty (still within 18 months). Total Schedule 18 penalty: £400.

Scenario C: filed 30 September 2028 (18 months late). Schedule 18 paragraph 17 flat-rate £400. Schedule 18 paragraph 18 tax-geared 10% × £36,000 = £3,600. Total Schedule 18 penalty: £4,000.

Scenario D: filed 30 March 2029 (24 months late). Schedule 18 paragraph 17 flat-rate £400. Schedule 18 paragraph 18 tax-geared 20% × £36,000 = £7,200. Total Schedule 18 penalty: £7,600.

Schedule 56 late-payment penalties stack independently from the payment due date of 1 January 2027: 5% at 31 January 2027, further 5% at 30 June 2027, further 5% at 31 December 2027. By the time Stoneleigh files under Scenario D (March 2029), the cumulative Schedule 56 penalty is 15% × £36,000 = £5,400, plus interest at the prevailing HMRC rate accrued daily over the 27-month period from due date to payment.

Combined Scenario D total: £7,600 (Schedule 18) + £5,400 (Schedule 56) + accrued interest. The penalty cost approaches 40% of the underlying CT liability before interest. For a director worried about short-term cash flow, the strategic point is that late filing compounds quickly through both penalty layers and the operational cost of working with HMRC on a settlement plan is materially lower than allowing the penalties to accrue.

Worked example 4: CIHC trap denying the small profits rate

Singh Lettings Ltd owns 3 BTL flats. Augmented profits £40,000, comfortably within the small profits rate band assuming single-company SPV status. The flats are let:

  • 2 to unconnected tenants at market rent (£10,800 each per year).
  • 1 to the founder's adult son at £3,600 per year (the market rent on comparable-evidence terms is £9,600).

The connected-tenant let at sub-market rent risks failing the section 18N(2)(b) qualifying-purpose carve-out and the section 18N(3) connected-tenant exclusion. HMRC's expansive reading of the carve-out treats the company as a close investment-holding company (CIHC) on these facts: the company is not wholly or mainly letting to unconnected persons on commercial terms.

The CT cost of CIHC classification on these facts:

  • Without CIHC (small profits rate): £40,000 × 19% = £7,600.
  • With CIHC (25% main rate, no marginal relief): £40,000 × 25% = £10,000.
  • CIHC cost: £2,400 per year, recurring annually until the connected-let position is fixed.

Remediation is operational: charge the son market rent (£9,600) on formal arm's-length terms. The son must afford the increased rent (or the company must accept lower distributable profits as a consequence of repaying him via salary or dividend). The CT saving (£2,400 per year) typically outweighs the increase in rental income brought to charge at the company level, but the planning involves more than just the headline numbers.

The wider point: the section 18N connected-tenant exclusion is interpreted expansively. A single below-market connected let can pull the whole company into CIHC, not just the connected-let portion. Property LtdCo operators with any below-market or connected-party lets should review their CIHC status with the next CT600 cycle.

Inaccuracy in the CT600: the Schedule 24 layer

Schedule 24 FA 2007 penalises inaccuracies within a CT600 that has been filed. The behaviour matrix is the same as for income tax self-assessment:

  • Careless behaviour: up to 30% of the under-assessed tax.
  • Deliberate but not concealed: up to 70%.
  • Deliberate and concealed: up to 100%.

The Schedule 24 paragraph 9 mitigation matrix mirrors the unprompted-vs-prompted floor architecture from Schedule 41: an unprompted disclosure of the inaccuracy accesses a lower mitigation floor than waiting for HMRC to discover the inaccuracy on enquiry. The offshore Category 1, 2, and 3 uplift under Schedule 24 paragraph 4A also applies to offshore-related CT understatements.

Schedule 24 and Schedule 18 paragraphs 17 and 18 can apply concurrently. A company that files a late CT600 containing inaccuracies attracts the Schedule 18 late-filing layer AND the Schedule 24 inaccuracy layer. The two layers operate on different fact patterns and the penalty stack adds rather than choosing between them.

Record retention under Companies Act 2006 section 388

Companies Act 2006 section 388 requires accounting records to be kept for 6 years from the end of the accounting period for private companies (3 years for public companies). The 6-year retention floor under CA 2006 is distinct from the 5-year-from-31-January floor for income tax under TMA 1970 section 12B.

For HMRC discovery purposes, FA 1998 Schedule 18 paragraphs 41 to 43 substitute for TMA 1970 section 29 in respect of company tax. The substantive time-limit framework reads across from the income-tax architecture: 4 years ordinary, 6 years careless, 20 years deliberate, 12 years offshore innocent error. A landlord LtdCo with 4 BTL SPVs should plan record retention at the longer of the CA 2006 6-year floor and the careless-behaviour 6-year discovery window, which align.

Appeals against CT penalties

Schedule 18 paragraph 17(5) provides a reasonable-excuse defence against the flat-rate late-filing penalty. The appeal route runs:

  1. To HMRC in writing within 30 days of the penalty notice, setting out the reasonable-excuse argument.
  2. HMRC review under TMA 1970 sections 49C to 49G if HMRC refuses.
  3. First-tier Tribunal under TMA 1970 section 31A read with the Tribunals, Courts and Enforcement Act 2007.

The First-tier Tribunal in HMRC v Hok Ltd [2012] UKUT 363 confirmed that the FTT cannot consider general fairness, only reasonable excuse and the statutory framework. Perrin v HMRC [2018] UKUT 156 sets the controlling four-stage reasonable-excuse test: identify the obligation, identify the excuse, assess whether the excuse is reasonable in the company's specific circumstances, assess whether the failure was remedied within a reasonable time of the excuse ceasing.

Reasonable excuses that typically succeed: serious illness of the company secretary or director responsible for filing, system failure (HMRC gateway outage, accounting software outage), unexpected events outside the company's control (theft of records, fire, flood). Reasonable excuses that typically fail: ordinary workload pressure, reliance on a third-party accountant that let the director down (unless reasonable care was exercised), forgetfulness, lack of cash flow.

The property-LtdCo CT discipline in summary

For a property LtdCo operator running one or more SPVs, the CT cycle has three operational disciplines:

  • Two deadlines per AP. CT payment at 9 months 1 day (small companies) or quarterly instalments (large); CT600 filing at 12 months. The two are independent; both must hit.
  • Associated-companies divisor testing at the start of each AP. Multi-SPV operators must compute the divisor and apply it to the £1.5m instalment threshold, the £20m very-large threshold, the £50,000 small-profits-rate band, and the £250,000 marginal-relief band. The divisor catches portfolio operators by surprise; the testing is straightforward but easily overlooked.
  • CIHC review on any below-market or connected-party lets. Section 18N's qualifying-purpose carve-out is narrow and the connected-tenant exclusion is interpreted expansively. A single below-market let can flip the whole company into CIHC and lose small-profits-rate access entirely.

If your property LtdCo structure has multiple SPVs, mixed connected and unconnected tenants, or a complex AP-alignment position from mid-year incorporations, we work with landlord-LtdCo and FIC operators on the deadline review, the instalment-threshold testing, the CIHC analysis, and the CT600 preparation and filing cycle.