diff --git a/app/models/Mortgage.ts b/app/models/Mortgage.ts
index f844c6a..67761ef 100644
--- a/app/models/Mortgage.ts
+++ b/app/models/Mortgage.ts
@@ -4,6 +4,13 @@ const DEFAULT_INTEREST_RATE = 0.06;
 const DEFAULT_MORTGAGE_TERM = 30;
 const DEFAULT_INITIAL_DEPOSIT = 0.15;
 
+interface MortgageParams {
+  propertyValue: number;
+  interestRate?: number;
+  mortgageTerm?: number;
+  initialDeposit?: number;
+}
+
 type MortgageBreakdown = {
   yearlyPayment: number;
   cumulativePaid: number;
@@ -29,21 +36,13 @@ export class Mortgage {
   totalMortgageCost: number;
   yearlyPaymentBreakdown: MortgageBreakdown;
 
-  constructor({
-    propertyValue,
-    interestRate = DEFAULT_INTEREST_RATE,
-    mortgageTerm = DEFAULT_MORTGAGE_TERM,
-    initialDeposit = DEFAULT_INITIAL_DEPOSIT,
-  }: {
-    propertyValue: number;
-    interestRate?: number;
-    mortgageTerm?: number;
-    initialDeposit?: number;
-  }) {
-    this.propertyValue = propertyValue;
-    this.initialDeposit = initialDeposit;
-    this.interestRate = interestRate;
-    this.termYears = mortgageTerm;
+  constructor(params: MortgageParams) {
+    this.propertyValue = params.propertyValue;
+    this.initialDeposit = params.initialDeposit || DEFAULT_INITIAL_DEPOSIT;
+    this.interestRate = params.interestRate || DEFAULT_INTEREST_RATE;
+    this.termYears = params.mortgageTerm || DEFAULT_MORTGAGE_TERM;
+
+    // Computed properties, order is significant
     this.principal = this.calculateMortgagePrinciple();
 
     const { monthlyPayment, totalMortgageCost } =
diff --git a/app/models/tenure/FairholdLandPurchase.ts b/app/models/tenure/FairholdLandPurchase.ts
index 2e8ee50..3d384ff 100644
--- a/app/models/tenure/FairholdLandPurchase.ts
+++ b/app/models/tenure/FairholdLandPurchase.ts
@@ -1,6 +1,17 @@
 import { Fairhold } from "../Fairhold";
 import { Mortgage } from "../Mortgage";
 
+interface FairholdLandPurchaseParams {
+  newBuildPrice: number;
+  depreciatedBuildPrice: number;
+  constructionPriceGrowthPerYear: number;
+  yearsForecast: number;
+  maintenanceCostPercentage: number;
+  incomeGrowthPerYear: number;
+  affordability: number;
+  fairhold: Fairhold;
+};
+
 type Lifetime = {
   maintenanceCost: number;
   landMortgagePaymentYearly: number;
@@ -13,47 +24,26 @@ export class FairholdLandPurchase {
   depreciatedHouseMortgage: Mortgage;
   lifetime: Lifetime;
 
-  constructor({
-    newBuildPrice,
-    depreciatedBuildPrice,
-    constructionPriceGrowthPerYear,
-    yearsForecast,
-    maintenanceCostPercentage,
-    fairhold,
-  }: {
-    newBuildPrice: number;
-    depreciatedBuildPrice: number;
-    constructionPriceGrowthPerYear: number;
-    yearsForecast: number;
-    maintenanceCostPercentage: number;
-    incomeGrowthPerYear: number;
-    affordability: number;
-    fairhold: Fairhold;
-  }) {
-    this.discountedLandPrice = fairhold.calculateDiscountedPriceOrRent();
+  constructor(params: FairholdLandPurchaseParams) {
+    this.discountedLandPrice = params.fairhold.calculateDiscountedPriceOrRent();
 
     this.discountedLandMortgage = new Mortgage({
       propertyValue: this.discountedLandPrice,
     });
 
     this.depreciatedHouseMortgage = new Mortgage({
-      propertyValue: depreciatedBuildPrice,
+      propertyValue: params.depreciatedBuildPrice,
     });
 
-    this.lifetime = this.calculateLifetime(
-      newBuildPrice,
-      maintenanceCostPercentage,
-      yearsForecast,
-      constructionPriceGrowthPerYear
-    );
+    this.lifetime = this.calculateLifetime(params);
   }
 
-  private calculateLifetime(
-    newBuildPrice: number,
-    maintenanceCostPercentage: number,
-    yearsForecast: number,
-    constructionPriceGrowthPerYear: number
-  ) {
+  private calculateLifetime({
+    newBuildPrice,
+    maintenanceCostPercentage,
+    yearsForecast,
+    constructionPriceGrowthPerYear,
+  }: FairholdLandPurchaseParams) {
     let newBuildPriceIterative = newBuildPrice;
     let maintenanceCostIterative = maintenanceCostPercentage * newBuildPrice;