How to use the Borrowing Power Calculator

A Borrowing Power Calculator estimates the maximum loan amount you are likely able to borrow by converting your income (less existing monthly debts) into a periodic repayment capacity and then using that capacity, together with the interest rate and loan term, to calculate the maximum loan an annuity repayment schedule will support.

Overview

This tool helps you estimate how much you could borrow from a lender based on:

• your gross income,
• existing monthly debt payments,
• the percentage of your income a lender will allow for debt repayments (serviceability or debt-service ratio),
• the expected annual interest rate, and
• the desired loan term and repayment frequency (monthly, fortnightly, weekly).

It uses a standard loan (annuity) math model to transform periodic repayment capacity into a present-value loan amount.

(Implementation note: the calculator’s HTML/JS structure and styling were inspired by your previously uploaded HTML calculator. html)

Inputs explained

• Gross Monthly Income: Your pre-tax monthly income the lender would consider (salary, wages, some regular bonuses, etc.).
• Current Monthly Debt Payments: Existing required monthly payments (credit card min payments, personal loans, leases). These reduce the amount available to service a new loan.
• Serviceability % / Lender Allowance: This is the share of your gross income a lender is willing to allow toward total debt obligations (existing debts + new loan repayment). Common values vary by lender and jurisdiction; the default in the calculator is 40% but lenders could use lower or higher percentages depending on risk, country rules, or your credit.
• Annual Interest Rate (%): The expected interest rate for the loan; the calculator converts it to a periodic rate based on the repayment frequency chosen.
• Loan Term (years): How long you want to pay the loan back.
• Repayment Frequency: Monthly (12), fortnightly (26), or weekly (52). This affects the interest compounding and the number of repayment periods.

What the calculator computes

1. Periodic repayment capacity = max(0, (serviceability% × GrossMonthlyIncome) − CurrentMonthlyDebtPayments)
   • This is how much per period (month/fortnight/week) is available to cover a new loan payment after accounting for your existing debts and the lender’s limit.
2. Maximum loan amount = Present value of an annuity with periodic payment = periodicCapacity × [(1 − (1 + r)^−n) / r]
   • where r = periodic interest rate = (annualRate / 100) / periodsPerYear
   • n = total number of periods = termYears × periodsPerYear
   • If r == 0 (zero interest) the formula simplifies to loan = periodicCapacity × n.

How to use the webpage calculator (step-by-step)

1. Open the borrowing-power-calculator.html file in a browser (double-click, or open with File → Open).
2. Enter your Gross Monthly Income.
3. Enter your Current Monthly Debt Payments (sum of all required monthly debt payments).
4. Set the Serviceability % — use your lender’s guideline if you know it, otherwise start with 35–45% as a typical range.
5. Enter the Expected Annual Interest Rate for the loan product you expect (or use a conservative slightly higher estimate than advertised rates).
6. Enter the Loan Term in years and pick repayment frequency.
7. Click Calculate Borrowing Power to see:
   • the estimated maximum loan amount,
   • the periodic repayment capacity,
   • input breakdown and periodic interest rate used.
8. If you want, in the “Repayment Estimate” area change the loan amount (for example to an actual property price) and click Monthly Repayment for Loan to see what the periodic repayment would be for that loan.

Worked example

• Gross monthly income: 5,000
• Current monthly debts: 500
• Serviceability: 40% → allowed for debt = 0.40 × 5,000 = 2,000
• Periodic capacity = 2,000 − 500 = 1,500 per month
• Annual rate = 6% → monthly r = 0.06 / 12 = 0.005
• Term = 25 years → n = 300 months

Loan ≈ 1,500 × (1 − (1 + 0.005)^−300) / 0.005 ≈ 1,500 × 166.791 ≈ 250,186 (rounded)

So the calculator would report roughly a 250k loan capacity (rounded and currency/display formatting dependent).

Notes & practical tips

• The calculator gives an estimate; actual lender assessments will include credit score, employment history, taxes, buffers (stress tests), fees, property value (for secured loans), and jurisdictional rules.
• Use a conservative interest rate (e.g., 1–2% higher than the advertised rate) to estimate stress-tested borrowing power.
• If lenders use net income (after tax) rather than gross, convert your input accordingly before using the calculator.
• For variable-rate loans, re-run the calculation with a higher rate to see the resilience of borrowing power.

FAQ (Borrowing Power Calculator)

Q: Is this number exact?
A: No — this is an estimate using standard annuity math and a simple serviceability rule. Actual lending decisions factor in credit history, employment stability, living expenses, tax, regulatory stress tests, LTV limits, fees and other lender-specific criteria.

Q: Which serviceability % should I use?
A: If you don’t know, try 35–45% as a starting range. Some conservative lenders may use 30–35% while others allow 45%+ depending on borrower profile and jurisdiction.

Q: Should I include bonuses and overtime in income?
A: Only include reliably recurring income that lenders will accept (often documented and proven). For variable income, lenders may average over 1–3 years or discount it.

Q: Why does the calculator ask for repayment frequency?
A: Because interest is converted to a periodic rate and number of periods depends on frequency — weekly/fortnightly schedules change the periodic rate and n which affect the math.

Q: What if interest rate is zero?
A: The script handles zero-interest case — the loan would simply be periodicCapacity × number_of_periods.

Q: Can this calculator handle non-annuity structures (interest-only, bullet)?
A: No — this calculator assumes standard amortizing loans (equal periodic payments of principal+interest). Interest-only or balloon payments need a different formula.

Q: How accurate are the payment rounding and formatting?
A: The calculator rounds results for display. For precise loan agreements lenders will compute exact schedules with their own rounding rules and fees.

Q: Can I change the currency?
A: The page displays numbers without a fixed currency symbol so it works for any currency. For local formatting you can add a currency symbol in the formatCurrency helper.

Disclaimer

This calculator provides a simplified estimate and educational guidance only. It does not constitute financial, legal, tax, or lending advice. Actual borrowing capacity is determined by individual lenders and regulators and may differ materially from the estimate produced here. Always consult with a qualified mortgage broker, bank lender or financial adviser for an official assessment tailored to your circumstances. The author and provider of this tool accept no liability for financial decisions made based on the results of this calculator.