UK Corporation Tax Calculator — connector documentation

MCP endpoint: https://uk-corp-tax-calc.connectorbay.com/mcp
REST API: POST https://uk-corp-tax-calc.connectorbay.com/v1/tools/{tool_name}, described by the OpenAPI 3.1 spec at https://uk-corp-tax-calc.connectorbay.com/openapi.json
Transport: Streamable HTTP, stateless, MCP specification 2025-06-18 or later
Authentication: none required. An optional Authorization: Bearer <key> raises rate limits.
Health: https://uk-corp-tax-calc.connectorbay.com/health · Tool schemas: https://uk-corp-tax-calc.connectorbay.com/tools.json
Publisher: Unify Dynamics LLC · connectorbay.com/uk-corp-tax-calc · agent@connectorbay.com

What UK Corporation Tax Calculator is for

UK Corporation Tax Calculator estimates the Corporation Tax of a UK company for one accounting period from the taxable profits you supply. corp_tax_estimate applies the 19% small profits rate up to GBP 50,000, the 25% main rate above GBP 250,000 and marginal relief in between using the HMRC formula (fraction 3/200 times the upper limit less augmented profits, times taxable profits over augmented profits), and it reproduces the worked example in HMRC's Company Taxation Manual. marginal_relief and effective_rate expose the relief and the resulting rate, associated_companies_adjustment divides the limits by one plus the number of associated companies (GOV.UK: 3 other companies give GBP 12,500 and GBP 62,500), and short_period_adjustment scales the limits for a period shorter than 12 months. company_deadlines returns the payment date (usually nine months and one day after the period end) and the Company Tax Return date (12 months after). rate_reference lists every rate, limit and rule with its GOV.UK or HMRC source, effective date and a verification label. Exact decimal arithmetic, local only, nothing stored or filed. General information only, not tax advice.

Ask your assistant things like:

"My company made GBP 90,000 of taxable profit in the year to 30 September 2026: how much Corporation Tax and how much marginal relief?"
"What is my effective Corporation Tax rate at GBP 180,000 of profit?"
"I own three companies: how do the small profits limits change?"
"Our first accounting period is only three months long: what are the limits for it?"
"When must I pay Corporation Tax and file the Company Tax Return for the year ending 31 March 2027?"
"What are the current Corporation Tax rates and limits, and how confident are you in them?"

What it does

corp_tax_estimate: Estimate Corporation Tax for one accounting period using the 19% small profits rate, the 25% main rate and marginal relief between the limits.
marginal_relief: Return the marginal relief in the band between the lower and upper profits limits, with the limits used.
effective_rate: Return the effective Corporation Tax rate (tax divided by taxable profits) for a profit figure.
associated_companies_adjustment: Divide the GBP 50,000 and GBP 250,000 limits by 1 plus the number of associated companies (12-month period).
short_period_adjustment: Return the marginal relief limits for an accounting period shorter than 12 months (days divided by 365).
company_deadlines: Return the Corporation Tax payment date (9 months and one day after the period end) and the Company Tax Return date (12 months after).
rate_reference: Return the Corporation Tax rates, limits, marginal relief fraction and deadline rules held here with source, effective date and verification label.

Data sources

Reference data from official sources (gov.uk); every answer states its source, date and validity period.

What it is not

UK Corporation Tax Calculator is independent; not affiliated with, endorsed by or operated by any government body, central bank, standards body or scheme operator. Names of rails, schemes and standards are used only to say what a tool works with. It is read-only: it never sends, pays, files or signs anything for you, and it never looks up private individuals.

Not advice. General information only, not legal, tax, accounting or payment advice. UK Corporation Tax Calculator is an independent tool: it is not affiliated with, endorsed by or operated by any government body, central bank, standards body or scheme operator. Rates, thresholds and rules change; check the cited official source and confirm with a qualified professional before you rely on a result.

Built for: GB. Languages: English.

Tools

Reference & guides

corp_tax_estimate — Estimate Corporation Tax for one accounting period using the 19% small profits rate, the 25% main rate and marginal relief between the limits. Use for "My company made GBP 90,000 profit in the year to 30 September 2026: how much Corporation Tax is that?". Args: taxable_profits, period_start, period_end, associated_companies, exempt_distributions.

marginal_relief — Return the marginal relief in the band between the lower and upper profits limits, with the limits used. Use for "How much marginal relief do I get on GBP 120,000 of profit?". Args: taxable_profits, period_start, period_end, associated_companies, exempt_distributions.

effective_rate — Return the effective Corporation Tax rate (tax divided by taxable profits) for a profit figure. Use for "What is my effective Corporation Tax rate on GBP 180,000 of profit?". Args: taxable_profits, period_start, period_end, associated_companies, exempt_distributions.

associated_companies_adjustment — Divide the GBP 50,000 and GBP 250,000 limits by 1 plus the number of associated companies (12-month period). Use for "I have two other companies under the same owner: how do the Corporation Tax limits change?". Args: associated_companies.

short_period_adjustment — Return the marginal relief limits for an accounting period shorter than 12 months (days divided by 365). Use for "Our first accounting period runs 1 January to 31 March: how are the Corporation Tax limits reduced?". Args: period_start, period_end, associated_companies.

company_deadlines — Return the Corporation Tax payment date (9 months and one day after the period end) and the Company Tax Return date (12 months after). Use for "When do I pay Corporation Tax and file the return for the year ending 31 March 2027?". Args: period_end.

rate_reference — Return the Corporation Tax rates, limits, marginal relief fraction and deadline rules held here with source, effective date and verification label. Use for "What are the current Corporation Tax rates and limits and where do they come from?". Args: on_date.

Conventions

Read-only. Every tool reads public data or computes; nothing is written anywhere and nothing about the user is stored.
Result envelope. ok: true with data, or ok: false with a structured error (bad_input, not_found, upstream_error). degraded lists optional sources that were unreachable.
Rate limits. Free tier 60 tool calls/minute and 300/day per user (keyed on the user identifier supplied by the host agent, else client IP); Pro keys raise this. Over-limit calls return HTTP 429 with Retry-After. initialize and tools/list are never counted.

Support

agent@connectorbay.com · connectorbay.com/uk-corp-tax-calc/support