@loanscope/math

Pure mortgage math primitives used by the LoanScope underwriting engine: amortization (calculatePMTFixed, calculateInterestOnlyPayment), LTV / DTI / CLTV, reserves resolution (with AUS-floor layering), qualifying income / payment policies, multi-borrower FICO blending, government fee schedules (FHA UFMIP + annual MIP, VA funding fee with IRRRL handling, USDA upfront + annual), closing-cost / property-tax / HOA / insurance / MI estimators, and effective program limits.

All math is performed via decimal.js under the hood; consumers receive branded primitives (Money, Ratio, etc.) from @loanscope/domain.

Install

pnpm add @loanscope/math @loanscope/domain

Usage

import {
  calculatePMTFixed,
  calculateLTV,
  calculateDTI,
  calculateFhaUfmip,
  calculateVaFundingFee,
} from "@loanscope/math";
import { LoanPurpose, money, months, ratePct } from "@loanscope/domain";

// Fully-amortizing monthly payment
const payment = calculatePMTFixed(money(500_000), ratePct(6.875), months(360));
// => Money — ~$3,285.31

// Loan-to-value ratio
const ltv = calculateLTV(money(500_000), money(625_000));
// => Ratio — 0.8

// Debt-to-income ratio (housing + liabilities / qualifying income)
const dti = calculateDTI(money(3_650), money(500), money(14_000));
// => Ratio — ~0.296

// FHA upfront mortgage insurance premium (1.75% of base loan)
const ufmip = calculateFhaUfmip({ loanAmount: money(500_000) });
// => Money — $8,750

// VA funding fee with IRRRL handling
const vaFee = calculateVaFundingFee({
  loanAmount: money(500_000),
  ltv,
  loanPurpose: LoanPurpose.IrrrlRefi,
  serviceContext: { priorUse: false, disabilityExempt: false, reserveOrGuard: false },
});
// => Money — $2,500 (0.5% IRRRL fixed rate)

Changelog

See CHANGELOG.md for per-package release history.

Part of the LoanScope monorepo

See the repository root for the full list of @loanscope/* packages and the architecture reference.

License

MIT