Agent

The affordability agent runs the lender’s own spreadsheet every time a number changes.

Checks whether the buyer can afford the mortgage, using the lender’s own spreadsheet. Whenever a number on the case changes, the agent re-runs it and tells whoever needs to know.

Book a demo Already have one?

MR-10421AffordabilityValuationDocumentsRationaleOfferAudit

Affordability dashboard

Pending

Product detailIs top slicing required

Lending typeResidential

Product5-year fixed 75%

Loan amount£179,000

Purchase price£250,000

LTV72%

Term15 years

Affordability calculationRunning your modelPass

Monthly surplus

Net income£4,200.00£4,020.00

Expenditure(£1,150.00)

Commitments(£650.00)

Mortgage payment(£1,380.00)

Remaining surplus£1,020.00£840.00

Monthly surplus stress test

Stressed rate7.00%

Stressed payment(£1,610.00)

Remaining surplus£790.00£610.00

Monthly incomeTotal net monthly£4,200.00£4,020.00

Tom Harris

Total net monthly£2,400.00

Total net annual£28,800.00

Payslips × 3

Emma Harris

Total net monthly£1,800.00£1,620.00

Total net annual£21,600.00£19,440.00

Payslips × 3Bank statement £180 lowerBank statement figure used

Affordability summary

v2.0

Net income£4,200.00£4,020.00p/m

Commitments£650.00p/m

Expenditure£1,150.00p/m

Mortgage£1,380.00p/m

Loan to income3.0x

Monthly surplus£1,020.00£840.00

Stressed surplus£790.00£610.00

Runs on this case

Run 2 · bank statement04 Mar, 10:42 · v2.0Pass

Run 1 · case submitted02 Mar, 09:15 · v2.0Pass

Illustrative example.

The goal

Everyone gets the same affordability answer, from the lender’s own spreadsheet, updated the moment the numbers change.

Your spreadsheet

Your Excel affordability model stays yours. We run it on the web.

Many lenders keep their affordability model in Excel, owned by the credit team. We keep it that way.

Keep your spreadsheet
Your Excel model stays the master copy. Your credit team still edits it.
EUC Lock hosts it
Locked, versioned and published: a calculator for brokers, an API for other systems.
Every system uses it
The broker portal, the underwriting system and the other agents all use the same model.

How it works

The agent re-runs your model when a number changes, then acts on the answer.

Three steps. Nobody has to ask for any of them.

1Watch

A number on the case changes, such as the buyer’s income.

Before: Someone has to notice, then re-run the spreadsheet.

Now: The agent sees the change as soon as a document is read.

Shown live: the income screen

MR-10421Affordability/IncomeValuationDocuments

Income

2 of 2 confirmed1 change found2 of 2 confirmed

Tom HarrisConfirmedTotal net monthly£2,400.00

Employment incomePAYEPayslips × 3 match the bank statement

Emma HarrisConfirmedChangedConfirmedTotal net monthly£1,800.00£1,620.00

Employment incomePAYE

Gross annual£25,500.00

Net monthly, payslips£1,800.00

Verified viaPayslips × 3

Bank statementReading£180 lower

Salary credit, January£1,620.00

Salary credit, February£1,620.00

Salary credit, March£1,620.00

Used for affordability£1,800.00 a month£1,620.00 a month

Affordability re-run started. The agent has sent the new income to your model. Nobody had to ask.

2Run

The agent re-runs your model and records the result.

Before: Figures copied into Excel by hand.

Now: The same figures go to your own model. Every run is kept with its version.

Shown live: your model’s API on EUC Lock

# Triggered by: bank statement read
POST /affordability   # your model, v2.0
{ "case": "MR-10421",
  "net_income": 4020, "commitments": 650,
  "expenditure": 1150, "loan": 179000,
  "term_years": 15 }

# Your model replies
{ "result": "pass", "surplus": 840,
  "stressed_surplus": 610, "stress_rate": 7.0,
  "max_loan": 246900, "model_version": "2.0" }

MR-10421AffordabilityRationaleAudit

Affordability runs

Model v2.0

Run 2 · bank statement read04 Mar 2026, 10:42 · surplus after the stress test £610Pass

Run 1 · case submitted02 Mar 2026, 09:15 · surplus after the stress test £790Pass

3Act

A pass needs no action. A fail goes to the people who must act.

Before: A failed check found at offer stage.

Now: The underwriter gets the figures. The broker gets the maximum loan before they resubmit.

Shown live: the credit report and the affordability dashboard

MR-10421Credit conductAffordabilityValuation

Credit conduct (Tom Harris)

Checking1 not declaredActions

Credit data received from the agency

Summary

Search date04 Mar 2026

Score610 · Good

Defaults / CCJs0 / 0

Active accounts

Open accounts4

Total balances£39,408

Worst status (24m)Up to date

Account information

Lender · accountOpenedBalanceMonthlyApplication

High street bankPersonal loanAug 2023£6,120£280CheckingDeclared

Card providerCredit cardMar 2019£1,850£120CheckingDeclared

Motor financeHire purchaseJan 2026£31,400£640CheckingNot declared

Mobile networkCommunicationsSep 2021£38£38CheckingNot counted

MR-10421AffordabilityValuationDocuments

Affordability calculation

v2.0PassRunning your modelFail

Monthly surplus

Net income£4,020.00

Expenditure(£1,150.00)

Commitments(£650.00)(£1,290.00)

Mortgage payment(£1,380.00)

Remaining surplus£840.00£200.00

Monthly surplus stress test

Stressed rate7.00%

Stressed payment(£1,610.00)

Remaining surplus£610.00(£30.00)

Fails the stress test by £30 a month. The maximum loan is now £175,700, which is £3,300 less than the £179,000 asked for.

Underwriter alerted: Jo WalshBroker told: Mark Evans, Evans & Co

Illustrative example. Field names depend on your model.

Case study

Cover: From Excel to Web – Securely Unlock Broker Affordability Checks Using Your Internal Excel Calculation Model

EUC Lock and CaturaFrom Excel to Web – Securely Unlock Broker Affordability Checks Using Your Internal Excel Calculation ModelRead the case study

Keep what works

Already have an affordability calculator? Keep it. Mortgage Rail connects to it.

Mortgage Rail doesn’t ask you to replace what works. If you already have this part, we connect to it. If you don’t, you can use ours.

If you already have one

Keep your own calculator. We connect it to the case.

If it already has an API, the agent uses it.
If not, we add one.
Brokers, underwriters and the buyer all see one answer.

If you don’t have one yet

Or use ours. Upload your Excel model and it runs as a web calculator.

EUC Lock hosts, locks and versions it.
A web calculator for brokers and an API for systems.
Every run recorded against the model version.

What comes into the affordability agent, and what goes out.

Comes in

Income and outgoings from the broker portal, documents and the credit report
Loan amount and term from the product agent

Affordability agent

Calls your model through its API when a number changes
Turns the reply into updates and alerts

Goes out

Pass or fail, maximum loan and surplus to broker, underwriter and buyer
A record of every run

The parts

All six parts of Mortgage Rail.

Mortgage Rail connects the systems and databases across the property industry. Each part does one job. Already have one? Keep it. If not, use ours.

Three places where people work

For the lender · where Mortgage Rail startedUnderwriting systemWhere the lender decides. Cases arrive checked, and the underwriter works the exceptions. It runs on top of the lender’s existing systems and replaces none of them.For the brokerBroker portalThe broker submits a case the lender can accept first time, with every document checked on upload.For the buyerCustomer portalThe buyer sees the application, the facts about the home and who is doing what.

Three agents that do the checking

This pageAffordability agentChecks the buyer can afford the loan, re‑running your own spreadsheet when the numbers change.

Valuation agentReads the valuer’s report on the property and sends each issue to whoever needs to act.Product agentFinds the mortgages that fit and keeps the list right as facts arrive.