Granny Flat Construction Loan Calculator

Why Use Lime Mortgage Brokers' Granny Flat Construction Loan Calculator

Model Your Construction Loan: Understand how your construction loan may work from the first drawdown through to project completion. Our calculator estimates interest-only repayments during construction before the loan transitions to principal and interest repayments once the granny flat is complete.
Understand Progress Payments: Construction loans are funded in stages rather than as a lump sum. Allocate your loan across the slab, frame, lock-up, fixing/fit-out, and completion stages to see how funds may be released throughout your build.
Plan Your Budget with Confidence: Enter your property value, existing mortgage balance, build contract price, deposit, interest rates, and loan term to estimate your construction loan and better prepare for the financial commitment of your granny flat project.
Adjust Different Loan Scenarios: Experiment with different deposits, interest rates, Loan-to-Value Ratios (LVR), loan terms, and progress payment amounts to understand how changes may affect your estimated repayments during and after construction.
Expert Guidance: Need help understanding your results? Our experienced mortgage brokers can explain your estimates, answer your questions, and help you explore construction loan options that suit your granny flat project.

How It Works:

Enter Your Property & Loan Details: Input your land or property value, existing mortgage balance, build contract price, deposit, interest rates, loan term, and maximum LVR.
Allocate Your Progress Payments: Divide your construction costs across each building stage, including the slab/base, frame, lock-up, fixing/fit-out, and completion stages.
Calculate Your Construction Loan: Instantly estimate your interest-only repayments during construction and your principal and interest repayments after the build is completed..
Review Your Results: Use your estimates to better understand your construction loan structure and prepare for each stage of your granny flat project.
Consult with an Expert: Speak with one of our mortgage brokers to discuss your results, verify your borrowing options, and receive personalised guidance before applying for construction finance.

Ready to Finance Your Granny Flat Build?

Take the guesswork out of construction finance with Lime Mortgage Brokers’ Construction Loan Finance Calculator. Model your construction loan, understand how progress payments work, and estimate your repayments throughout every stage of your granny flat build. When you’re ready, our experienced mortgage brokers are here to help you find the right construction finance solution for your goals.

Construction Loan Details

Set your land value, construction cost, progress payments and rates

How construction loans work: Funds are released in progress payments as each stage of the build is completed. During construction you pay interest only on the drawn balance. Once complete, the loan converts to a standard principal & interest mortgage.

Land / Property Value

Existing Mortgage Balance

Total Build Contract Price

Deposit (cash contribution)

Construction Interest Rate (p.a.)

6.50%

P&I Rate After Completion (p.a.)

6.25%

P&I Loan Term (years)

30 yrs

Max LVR (lender limit)

80%

Progress Payment Stages

Adjust the amount drawn at each construction stage. The total must equal the loan amount (contract price minus deposit).

Stage Draw Amount % of Loan

1Slab / Base

—

2Frame

—

3Lock-up

—

4Fixing / Fit-out

—

5Completion

—

P&I Monthly Payment
—
On total debt, after construction ends

Loan Amount

—

Contract − deposit

Total Debt

—

Incl. existing mortgage

End-of-Build LVR

—

Post-construction

Total Interest (P&I phase)

—

Over full term, on total debt

Construction Interest

—

Interest-only phase

Construction Drawdown — Interest-Only Costs Per Stage

Stage	Drawdown	Cumulative Balance	Monthly Interest	Est. Duration	Stage Interest Cost

Annual P&I Repayment Breakdown (Post-Build, Total Debt)

Year	Opening Balance	Principal Paid	Interest Paid	Closing Balance

Important: This calculator is for illustrative purposes only and does not constitute financial advice. Construction interest costs assume each stage draws the stated amount and is held for the estimated duration before the next drawdown. Actual durations, drawdown timing, and interest calculations will vary based on your lender and builder. The post-construction P&I repayment and amortisation schedule are calculated on the combined total debt (existing mortgage balance plus the construction loan amount), assuming both are consolidated onto the P&I rate and term entered above. Always engage a licensed mortgage broker for full borrowing capacity and loan structuring advice.

Apply for the finance that you need

Lime Mortgage Broker Reviews

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   Based on 67 reviews 
    
 
 
 
   
 
 
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   Anabelle Williams 
 
 
 
 Trustindex verifies that the original source of the review is Google. Can’t thank Shawn and his team enough for helping us with our first mortgage 4 years ago and refinancing just recently! We really appreciate that he goes above and beyond to assist and his quick service turnaround time.  He is always so helpful and friendly when answering my many questions. He applies his strong expertise in a professional and effective way for you to understand. Can’t recommend him enough..Best in the biz!
  
 
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   Carmela Verzini 
 
 
 
 Trustindex verifies that the original source of the review is Google. Our experience with Lime Mortgage brokers has been absolutely fantastic, they have been so helpful with their assistance, advice and support. Thankyou Shawn for all your time, phone calls and always making sure that we receive the best opportunity to accomodate our needs, Lydia has also been so amazing with all the updates and explaining situations when we were unsure about something. I will always highly recommend Lime Mortgage Brokers to anyone in need, because we know that we can always rely on wonderful and caring support and advice. Thankyou Shawn, Thankyou Lydia, Best Wishes always Enzo and Carmela Verzini
  
 
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   Dean Innes 
 
 
 
 Trustindex verifies that the original source of the review is Google. Shawn was amazing when helping me find finance for my property. This was my first time dealing with banks and Shawn was always available to help. The team at Lime Mortgage Brokers were attentative, efficient and proffesional. Couldn't ask for much more! Highly recommend.
  
 
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   Ella Schooling 
 
 
 
 Trustindex verifies that the original source of the review is Google. Made the impossible ' possible for me and my family . Amazing team and so easy to deal with .  Thankyou shawn
  
 
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   andrew ward 
 
 
 
 Trustindex verifies that the original source of the review is Google. Shawn and Lydia from Lime Mortgage Brokers made the whole process easy from start to finish. They were proactive, knowledgeable, and really took the time to understand what we needed. Communication was excellent, and we felt supported every step of the way. We’re extremely happy with the outcome and wouldn’t hesitate to use them again or recommend them to others. Thanks again Andrew & Talie
  
 
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   Savanna Oats 
 
 
 
 Trustindex verifies that the original source of the review is Google. Excellent service, quick to respond and Shawn and Lydia are very genuine -  I felt that they had my best interests in mind when helping me refinance.
  
 
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   sean kirsten 
 
 
 
 Trustindex verifies that the original source of the review is Google. Shaun was very easy to deal with answered all questions and couldn’t be happier with the results highly recommend.
  
 
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   Isabelle Wheeler 
 
 
 
 Trustindex verifies that the original source of the review is Google. Lydia and Shawn were very helpful and approachable throughout the process of us refinancing. We were very happy with their service and would recommend their services to anyone seeking assistance in this financial field. Thanks Lydia and Shawn!
  
 
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   MG 
 
 
 
 Trustindex verifies that the original source of the review is Google. If you're looking for a mortgage broker in Perth, then I would strongly recommend Lime - Shawn and team go above and beyond the usual service to find an optimal solution.
  
 
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   Amy Collins 
 
 
 
 Trustindex verifies that the original source of the review is Google. I've been using Shawn for 15 years during my multiple house moving! Very patient, helpful and knowledgeable to ensure we find the best outcome. Highly recommend him!

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