Buy-to-let company tax: the questions landlords actually ask

Updated July 2026

Do I need an accountant to file my company's tax return?

Legally, no — a director can file. Practically, it depends on the year. A plain year (rent in, expenses out, one mortgage, no purchases or sales) is genuinely self-serviceable with the right software. A year with a property purchase or disposal, or money borrowed from the company, is not. Our comparison guide is blunt about which is which.

Can I still file for free on the HMRC website?

No. HMRC's free service closed permanently on 31 March 2026; every company must now file through commercial software. Here's what changed and what to do. Our first filing is free, which for many single-property companies restores roughly what CATO used to be.

What actually gets filed, and where?

Two places. HMRC gets the Company Tax Return — CT600 form, tax computation and full accounts, all iXBRL-tagged — within 12 months of your period end. Companies House separately gets the micro-entity accounts within 9 months. The Companies House half is a 10-minute job we walk you through.

When is the tax actually due?

Before the return is: 9 months and 1 day after your period end. For a 31 March 2026 year end that's 1 January 2027. File early so you know the number in good time.

Is my buy-to-let mortgage interest tax deductible?

In a company, yes — in full, against the property profit. The Section 24 restriction that hits personal landlords does not apply to companies. Only the interest, never the capital repayment. Rates and a worked example here.

How much corporation tax will my company pay?

19% on taxable profits up to £50,000; marginal relief between £50,000 and £250,000; 25% above. The thresholds shrink if you control other companies. The calculator applies the exact rules to your numbers.

My company is dormant — do I still file?

HMRC usually issues a "notice to deliver" only to active companies; if you've told HMRC the company is dormant, no CT600 is normally due. Companies House accounts (dormant accounts) are still due every year regardless. If HMRC has sent a notice to deliver, you must file even for a nil year.

What if my company made a loss this year?

You still must file, and the loss is valuable — it carries forward automatically and reduces future years' tax. FileMyRent handles loss years: the return records the loss, carries it forward, and next year's return sets it against your profit. The live preview shows exactly how much is banked.

What is iXBRL and why do I care?

Inline XBRL is a machine-readable tagging format HMRC requires for accounts and computations — every figure carries an invisible label HMRC's systems validate. You care only because it's why a home-made PDF can't be filed. Software (ours included) generates it; you never touch it.

My company's first period is longer than 12 months — what happens?

Companies House sets a first period that's often 12 months plus a few days, which means two CT600s (one for the first 12 months, one for the remainder). FileMyRent handles this automatically: one interview, and we prepare both returns — profits apportioned by days, one set of accounts covering the whole period, and each return's own payment deadline shown clearly.

What are the penalties if I'm late?

HMRC: £100 immediately, another £100 at three months, tax-geared penalties from six months — plus interest on late-paid tax. Companies House: £150 rising to £1,500, doubling if you're late two years running. The two run independently; being late at both compounds.