Suites · lending
Lending and loans
Loans from quote to redemption: level repayments, amortisation schedules, APR, daily interest, overpayments, early settlement, affordability and LTV.
64 capabilities (27 core, 37 optional) and 13 gaps, in build order. Put each line in the file that calls it, then fune build.
Not financial advice. APR and early settlement follow the UK Consumer Credit Act rules (FCA CONC); a regulated lender must have its compliance team confirm how the app uses them.
TypeScript Python Rust
1. Quotes and repayments
Price a loan: the regular repayment and what it costs in total.
lending.loan-payment core Unreviewed
The level (annuity) repayment for a principal, rate and term, rounded the way you choose.
Level repayment for a loan (annuity formula), computed exactly and rounded once, the way you choose.
import { loanPayment } from "#fune/lending.loan-payment@^1" ;
1.0.1
lending.apr core Unreviewed
The consumer-credit APR from drawdowns and repayments by the FCA CONC equation, for quotes and agreements.
Consumer-credit APR from drawdowns and repayments, by the FCA CONC App 1.2.6 equation, to one decimal place.
import { apr } from "#fune/lending.apr@^1" ;
1.0.1
finance.compound-interest optional
Compound interest accrued period by period in minor units, for savings-style or interest-only illustrations.
Compound interest accrued period by period in minor units, the way a statement is built.
import { compoundInterest } from "#fune/finance.compound-interest@^1" ;
1.0.0
2. Schedules and interest
Lay out each period's interest, principal and balance, and accrue interest on a changing balance.
lending.amortisation-schedule core Unreviewed
Per-period interest, principal and balance for a level-payment loan, ending at exactly zero.
Repayment schedule for a level-payment loan: interest, principal and balance per period, ending at exactly zero.
import { amortisationSchedule } from "#fune/lending.amortisation-schedule@^1" ;
1.0.1
lending.daily-interest core Unreviewed
Interest accrued day by day on a changing balance under a day-count convention.
Interest accrued day by day on a changing balance under a day-count convention, summed exactly and rounded once.
import { dailyInterest } from "#fune/lending.daily-interest@^1" ;
1.0.1
dates.day-count-fraction optional
Year fraction by ACT/365F, ACT/360, 30/360 or ACT/ACT, for the interest convention.
Year fraction between two dates by ACT/365F, ACT/360, 30/360, 30E/360 or ACT/ACT ISDA, as an exact fraction.
import { dayCountFraction } from "#fune/dates.day-count-fraction@^1" ;
1.0.0
finance.uk-bank-rate optional
Bank of England Bank Rate on a date, for tracker and variable-rate loans set over base.
Bank of England Bank Rate (base rate) in force on a date, from the Bank's official history since 2001.
import { ukBankRate } from "#fune/finance.uk-bank-rate@^1" ;
1.0.1
3. Overpayments and settlement
Answer what happens when a borrower pays more or pays off early.
lending.early-settlement core Unreviewed
Settlement figure and rebate on UK regulated consumer credit under the 2004 Early Settlement Regulations.
Early settlement figure and rebate on UK regulated consumer credit, per the Early Settlement Regulations 2004.
import { earlySettlement } from "#fune/lending.early-settlement@^1" ;
1.0.1
lending.overpayment-effect optional Unreviewed
What a one-off overpayment does: a shorter term at the same payment, or a lower payment.
What a one-off overpayment does to a loan: a shorter term at the same payment, or a lower payment over the same term.
import { overpaymentEffect } from "#fune/lending.overpayment-effect@^1" ;
1.0.1
4. Affordability and underwriting
Decide whether a borrower can afford the loan.
lending.affordability core Unreviewed
Debt-to-income and a stressed-rate affordability test for the new loan's monthly repayment.
Debt-to-income and a stressed-rate affordability test for a proposed loan's monthly repayment.
import { affordability } from "#fune/lending.affordability@^1" ;
1.0.1
lending.ltv optional Unreviewed
Loan-to-value in basis points and its band from your band table, for secured lending.
Loan-to-value ratio in basis points, and the band it falls in from a band table you supply.
import { loanToValue } from "#fune/lending.ltv@^1" ;
1.0.1
property.mortgage-affordability optional Unreviewed
Mortgage income multiple and stress-tested repayment against income, for residential mortgages.
Mortgage affordability: the loan-to-income multiple and a stress-tested repayment against income, both checked.
import { mortgageAffordability } from "#fune/property.mortgage-affordability@^1" ;
1.0.1
credit-checks Credit reference agency searches (Experian, Equifax, TransUnion) and scoring: network services and a credit policy caps does not have.open-banking-income Verifying income and outgoings from bank data (Open Banking, payslips): caps checks figures you already have.
5. Payments and collections
Take repayments by Direct Debit and validate the account they come from.
banking.bacs-processing-date optional
Bacs input and arrival dates for a Direct Debit collection, skipping weekends and bank holidays.
Bacs three-day cycle: input, processing and entry (arrival) dates for a submission, skipping weekends and bank holidays.
import { bacsProcessingDates } from "#fune/banking.bacs-processing-date@^1" ;
1.0.0
subscriptions.dunning-schedule optional
Retry dates for a failed repayment from a retry policy.
Retry dates for a failed subscription payment from a retry policy, in calendar or business days.
import { dunningSchedule } from "#fune/subscriptions.dunning-schedule@^1" ;
1.0.0
arrears-handling Arrears, forbearance and default notices (CCA notices of sums in arrears, default notices): the rules and letters are yours.direct-debit-mandates Setting up and submitting Direct Debit mandates and collections (Bacs files or a provider like GoCardless).
Hold money as currency-tagged integer minor units and do plain arithmetic on it safely.
money.amount core
The Money type ({ minor, currency }) every other money capability takes and returns.
A currency-tagged monetary amount held in integer minor units.
import { money } from "#fune/money.amount@^1" ;
1.0.2
money.add core
Adds and subtracts amounts, refusing to mix currencies by accident.
Add, subtract and negate monetary amounts, refusing to mix currencies.
import { addMoney } from "#fune/money.add@^1" ;
1.0.1
money.sum core
Totals a list of amounts, with an explicit currency for an empty list.
Total a list of monetary amounts, with an explicit currency for the empty case.
import { sumMoney } from "#fune/money.sum@^1" ;
1.0.1
money.compare core
Compares, mins, maxes and clamps amounts of one currency without unwrapping them.
Compare two amounts of one currency, refusing to compare across currencies; min, max and clamp too.
import { compareMoney, minMoney, maxMoney, clampMoney } from "#fune/money.compare@^2" ;
2.0.04 functions
7. Rates and rounding from money-basics
Apply percentages and divide amounts with the rounding stated, never a float.
money.apply-rate core
Applies a basis-point rate (VAT, discount, commission) to an amount with explicit rounding.
Apply a rate expressed in basis points to a monetary amount, with an explicit rounding mode.
import { applyRate } from "#fune/money.apply-rate@^1" ;
1.0.1
math.round-div core
Integer division with a named rounding mode, for any money maths the others do not cover.
Integer division with an explicit rounding mode, for money arithmetic that must not drift.
import { roundDiv } from "#fune/math.round-div@^1" ;
1.0.0
math.basis-points optional
Converts "12.5%" to and from basis points exactly, for rates typed in by users.
Convert a rate between percent, basis points and a plain ratio exactly, as decimal text or integer basis points.
import { convertRate, toBasisPoints, fromBasisPoints } from "#fune/math.basis-points@^2" ;
2.0.03 functions
math.percent-change optional
Percentage change between two figures in basis points, for "up 4.2% on last month".
Percentage change from one value to another, in basis points, with an explicit rounding mode.
import { percentChange } from "#fune/math.percent-change@^1" ;
1.0.0
math.rational optional
Exact fractions for rates that must not drift across many steps.
Exact fraction arithmetic, always reduced, for rates and ratios that must not drift.
import { calculateRational, rational, addRational, subtractRational, multiplyRational, divideRational, compareRational, rationalToInteger } from "#fune/math.rational@^2" ;
2.0.08 functions
math.round-div-big optional
Rounded division on numbers past 2^53, for very large totals.
Divide two integers of any size with an explicit rounding mode, on decimal strings, for exact money sums past 2^53.
import { roundDivBig } from "#fune/math.round-div-big@^1" ;
1.0.0
Divide an amount between people, periods or lines so the parts add back to the whole.
money.allocate core
Splits an amount by ratios (60/40, by quantity) without losing or inventing a penny.
Split an amount across ratios without losing or inventing a single minor unit.
import { allocate } from "#fune/money.allocate@^1" ;
1.0.1
money.split-even optional
Splits an amount into n near-equal parts that sum exactly, for instalments or shares.
Split an amount into n near-equal parts that add back up to exactly the whole.
import { splitEven } from "#fune/money.split-even@^1" ;
1.0.0
9. Display and input from money-basics
Show amounts to people and read what they type.
money.format core
Renders an amount as text with the currency's real number of decimal places.
Render a monetary amount as text, using the currency's real minor-unit precision.
import { formatMoney } from "#fune/money.format@^1" ;
1.0.0
money.parse optional
Reads "£1,234.50" or "1.234,50 €" typed by a user into minor units, strictly.
Parse "£1,234.50" or "1.234,50 €" into integer minor units, strictly: no guessing, no rounding.
import { parseMoney } from "#fune/money.parse@^1" ;
1.0.0
money.currency-digits optional
How many decimal places each ISO 4217 currency has, for input boxes and validation.
How many decimal places a currency's minor unit has, from the ISO 4217 list.
import { currencyDigits } from "#fune/money.currency-digits@^1" ;
1.0.0
10. Other currencies from money-basics
Convert between currencies at a rate you hold.
money.convert optional
Converts an amount at a supplied exact rate with explicit rounding.
Convert an amount to another currency at a supplied exact rate, with an explicit rounding mode.
import { convertMoney } from "#fune/money.convert@^1" ;
1.0.0
11. Calendar arithmetic from dates-basics
Move and measure ISO dates exactly, with no date library and no clock reads.
dates.add-days core
Shifts a date by whole days, for due dates and windows.
Shift an ISO date by a whole number of days, forwards or backwards, with exact calendar arithmetic.
import { addDays } from "#fune/dates.add-days@^1" ;
1.0.0
dates.add-months core
Adds months clamping to month end, so 31 January plus a month is the end of February.
Add calendar months to an ISO date, clamping to the month end: 31 Jan + 1 month is 28 or 29 Feb.
import { addMonths } from "#fune/dates.add-months@^1" ;
1.0.0
dates.days-between core
Signed calendar days between two dates, for ages of invoices and stays.
Calendar days from one ISO date to another, signed: negative when the second date is earlier.
import { daysBetween } from "#fune/dates.days-between@^1" ;
1.0.0
dates.month-boundaries core
First and last day of a date's month, for monthly periods and statements.
The first day, last day and length of the calendar month containing a date.
import { monthBoundaries } from "#fune/dates.month-boundaries@^1" ;
1.0.0
dates.day-of-week core
ISO weekday of a date, for weekend rules and opening hours.
The ISO 8601 day of the week for a date: 1 is Monday through 7 is Sunday.
import { dayOfWeek } from "#fune/dates.day-of-week@^1" ;
1.0.0
dates.is-leap-year optional
Whether a year is a leap year, for 365/366-day calculations.
Whether a year is a Gregorian leap year: every 4th, except centuries, except every 400th.
import { isLeapYear } from "#fune/dates.is-leap-year@^1" ;
1.0.0
dates.overlap optional
Days two date ranges share, for prorating and clash checks.
Days two date ranges have in common, with the end of each range stated as inclusive or exclusive.
import { overlapDays } from "#fune/dates.overlap@^1" ;
1.0.0
dates.age optional
Age in whole years on a date, handling 29 February birthdays.
Age in whole years on a given date, with 29 February birthdays ageing on 1 March in other years.
import { age } from "#fune/dates.age@^1" ;
1.0.0
12. Periods and reporting dates from dates-basics
Put dates into the periods reports are grouped by.
dates.quarter core
Calendar and fiscal quarter of a date for any year-start month.
Calendar quarter and fiscal quarter of a date, with the fiscal year and quarter date ranges, for any start month.
import { quarter } from "#fune/dates.quarter@^1" ;
1.0.0
dates.week-number optional
ISO week number and week-year, for weekly reports.
ISO 8601 week number and week-numbering year of a date: weeks start Monday, week 1 holds the first Thursday.
import { weekNumber } from "#fune/dates.week-number@^1" ;
1.0.0
13. Working days and holidays from dates-basics
Skip weekends and public holidays when counting or adding days.
dates.bank-holidays core
UK bank holidays for a region and year, as gov.uk publishes them.
UK bank and public holidays for a region and year, as published by gov.uk, including one-off holidays.
import { bankHolidays } from "#fune/dates.bank-holidays@^1" ;
1.0.1
dates.add-business-days core
Moves a date by working days, skipping weekends and a holiday list.
Move a date forward or back by working days, skipping weekends and a caller-supplied holiday list.
import { addBusinessDays } from "#fune/dates.add-business-days@^1" ;
1.0.0
dates.business-days-between core
Working days between two dates, for SLAs and notice periods.
Working days between two dates, excluding weekends and a caller-supplied holiday list.
import { businessDaysBetween } from "#fune/dates.business-days-between@^1" ;
1.0.0
14. Repeating schedules from dates-basics
Generate the dates of something that repeats.
dates.recurrence optional
The next n dates of a rule: monthly on the 31st, last Friday, every two weeks.
The next n dates of a repeating rule: monthly on a day, last weekday of the month, every k days or weeks, yearly.
import { recurrence } from "#fune/dates.recurrence@^1" ;
1.0.0
15. Times and durations from dates-basics
Work with times of day, durations and timestamps.
time.duration optional
Parses and adds durations like 1h30m in whole minutes, and formats the total.
Parse durations written as 1h30m, 90m or 01:30, add them up in whole minutes, and format the total.
import { duration } from "#fune/time.duration@^1" ;
1.0.0
time.minutes-between optional
Minutes between two local date-times, across midnight.
Minutes from one local date and time to another, correct across midnight; wall-clock time, no time zones.
import { minutesBetween } from "#fune/time.minutes-between@^1" ;
1.0.0
time.round-to-increment optional
Rounds minutes to a billing increment such as 6 or 15.
Round a duration in minutes to a billing increment such as 6 or 15 minutes, up, down or to nearest.
import { roundToIncrement } from "#fune/time.round-to-increment@^1" ;
1.0.0
time.iso-to-unix optional
RFC 3339 timestamps to Unix seconds.
An RFC 3339 timestamp with a Z or offset, such as 2026-09-26T13:00:00+01:00, to Unix time in whole seconds.
import { isoToUnix } from "#fune/time.iso-to-unix@^1" ;
1.0.0
time.unix-to-iso optional
Unix seconds to an ISO 8601 UTC timestamp.
Unix time in seconds to an ISO 8601 UTC timestamp such as 2026-09-26T12:00:00Z, for years 0001 to 9999.
import { unixToIso } from "#fune/time.unix-to-iso@^1" ;
1.0.0
time.countdown optional
Seconds left until a moment and a 4:05 style timer text.
Seconds left until a Unix time, whether it has passed, and a timer text like 4:05, for tokens or retry waits.
import { countdown } from "#fune/time.countdown@^1" ;
1.0.0
Check payee and customer bank details before money moves.
validation.iban core
Checks an IBAN's mod-97 checksum and its country's length.
Check an IBAN against the ISO 13616 mod-97-10 checksum and the registered length for its country.
import { isIban } from "#fune/validation.iban@^1" ;
1.0.0
validation.bic optional
Checks a SWIFT/BIC code's format and splits it.
Check the format of a SWIFT/BIC code (8 or 11 characters) and split it into its parts.
import { validateBic } from "#fune/validation.bic@^1" ;
1.0.0
validation.uk-sort-code-account optional
Checks a UK sort code and account number by the Vocalink modulus rules, against a table you supply.
Check a UK sort code and account number with the Vocalink/Pay.UK modulus rules, against a table you supply.
import { validateUkSortCodeAccount } from "#fune/validation.uk-sort-code-account@^3" ;
3.0.0
validation.uk-modulus-table optional
Parses Vocalink's VALACDOS and SCSUBTAB files into that table.
Parse Vocalink's VALACDOS.txt and SCSUBTAB.txt into the table UK sort code modulus checking needs.
import { parseUkModulusTable } from "#fune/validation.uk-modulus-table@^1" ;
1.0.0
18. Identifiers and check digits from validation-basics
Catch mistyped reference numbers by their check digits.
validation.luhn optional
Luhn mod-10 check, for card numbers and many reference numbers.
Check a digit string against the Luhn mod-10 checksum used by payment cards and many identifiers.
import { isLuhn } from "#fune/validation.luhn@^1" ;
1.0.0
validation.uk-company-number optional
Checks a Companies House number's format and prefix.
Check a Companies House company number's format and prefix (SC, NI, OC, LP...) and zero-pad it to eight characters.
import { validateUkCompanyNumber } from "#fune/validation.uk-company-number@^2" ;
2.0.1
validation.lei optional
Checks a Legal Entity Identifier's check digits.
Check a 20-character Legal Entity Identifier against its ISO 17442 / ISO 7064 MOD 97-10 check digits.
import { validateLei } from "#fune/validation.lei@^1" ;
1.0.0
validation.gtin optional
Checks an EAN/UPC/GTIN barcode number.
Check an EAN-8, UPC-A, EAN-13 or GTIN-14 barcode number against the GS1 mod-10 check digit.
import { validateGtin } from "#fune/validation.gtin@^1" ;
1.1.0
19. Displaying sensitive values from validation-basics
Show stored identifiers without exposing them.
text.mask optional
Masks all but the last digits of a card, account or phone number.
Mask all but the last n characters of a card, account or phone number, optionally keeping separators.
import { mask } from "#fune/text.mask@^1" ;
1.0.0
Gaps What this kind of app usually needs that Functional Weave does not have yet: write these yourself, or use a service.
agreement-documents Pre-contract information (SECCI) and credit agreement documents: caps computes the figures, not the regulated documents.fx-rate-source Where exchange rates come from: money.convert takes a rate you supply; fetching and storing daily rates (ECB, a provider's API) is yours.money-storage Storing amounts: the database columns (integer minor units plus a currency code) and their migrations are yours.time-zones Time zones and daylight saving: caps works in ISO dates, UTC and wall-clock times; converting with the IANA tz rules is yours.locale-formatting Showing dates in a user's language and format ("3 octobre 2026"): caps returns ISO dates, not localised text.non-uk-holidays Public holidays outside the UK: dates.bank-holidays is UK only; pass another country's list to the working-day functions yourself.address-lookup Turning a postcode into a list of addresses (Royal Mail PAF or a lookup API) is network work and not in caps.email-deliverability Whether a mailbox exists (MX lookups, a confirmation email): validation.email checks the syntax only.vocalink-data The Vocalink modulus tables themselves: download them from Pay.UK under its terms; caps parses them but does not ship them.