Co-Buying Calculator
Buying a property with family, friends, a partner or another investor can make home ownership more achievable, but it also raises important questions. How should the deposit be split? What happens if one person contributes more than the others? Should ownership match the deposit, the ongoing repayments, or something else?
The Fundd Co-Buying Calculator helps answer these questions by modelling each buyer’s financial contribution and comparing different ownership structures. Whether you’re buying with two, three or four people, the calculator estimates a fair ownership split based on the contributions you agree should count.
Everything runs securely within your browser, so your information stays on your device while results update instantly as you adjust the figures.
What does the Co-Buying Calculator calculate?
The calculator estimates how each buyer contributes towards purchasing and owning a property over time.
Based on your inputs, it calculates:
- Total acquisition costs
- Total cash required from all buyers
- Monthly mortgage repayments
- Each buyer’s upfront contribution
- Each buyer’s ongoing repayment contribution
- Suggested ownership percentages
- Projected property equity over time
- Estimated equity available after selling costs
- Each buyer’s share under different ownership structures
Rather than assuming ownership should simply be split equally, the calculator allows you to compare equal ownership, custom ownership and contribution-based ownership.
How the Co-Buying Calculator works
Step 1: Enter the property details
Begin by entering:
- Purchase price
- Current estimated property value
- Loan amount
- Loan term
- Interest rate
The calculator uses this information to estimate the required mortgage repayment and the total amount needed to complete the purchase.
Step 2: Add each buyer
You can add between two and four buyers.
For each buyer, enter:
- Cash deposit
- Purchase costs paid
- Other upfront contributions
- Ongoing repayment contribution
The calculator tracks each person’s financial contribution separately throughout the ownership period.
Step 3: Choose an ownership method
You can compare three different approaches:
- Equal ownership
- Custom ownership percentages
- Contribution-based ownership
Contribution-based ownership can be calculated using:
- Upfront contributions only
- Upfront contributions plus principal repaid
- Total cash contributed (including interest)
This allows buyers to choose the approach that best reflects their agreement.
Step 4: Project future equity
The calculator projects:
- Future property value
- Remaining loan balance
- Selling costs
- Net equity
It then compares how that equity would be divided under each ownership method.
Why is calculating fair ownership important?
One of the most common issues in co-buying arrangements is assuming that ownership should simply be split evenly.
In reality, buyers often contribute different amounts towards:
- Deposits
- Stamp duty
- Legal costs
- Loan repayments
- Renovations
- Other expenses
Without discussing these differences before purchasing, disagreements can arise later if the property is sold or one owner wants to exit.
Using a contribution-based ownership model can help buyers have clearer conversations before entering into a co-ownership arrangement.
Should ownership match the deposit?
Not necessarily.
Some co-buyers prefer ownership to reflect:
- Deposit contributions only
- Total upfront costs
- Ongoing mortgage repayments
- Total cash invested over time
There is no single “correct” approach.
The calculator allows you to compare several ownership methods side by side so you can see how different agreements may affect each person’s equity.
Can unequal mortgage repayments change ownership?
They can, depending on the agreement between the buyers.
If one buyer contributes significantly more towards mortgage repayments over many years, some co-buyers believe ownership should gradually reflect those additional contributions.
Others prefer ownership percentages to remain fixed regardless of who contributes more.
The calculator illustrates both approaches so buyers can better understand the financial implications.
What happens if one buyer pays more?
If one buyer contributes more towards the deposit, purchase costs or mortgage repayments, the contribution-based ownership calculation will generally allocate a larger suggested ownership percentage to that buyer.
This can provide a useful starting point for discussions before purchasing a property together.
Who should use this calculator?
This calculator may be useful if you are:
- Buying a property with your partner
- Purchasing with friends
- Buying with siblings
- Purchasing with parents or children
- Investing with multiple buyers
- Using a shared equity arrangement
- Comparing different ownership structures
- Preparing a co-ownership agreement
Frequently Asked Questions
What is a co-buying calculator?
A co-buying calculator estimates how ownership of a property could be divided based on each buyer’s financial contribution. It can compare equal ownership, custom ownership percentages and contribution-based ownership over time.
How do you calculate ownership when buying a house together?
Ownership can be divided equally, agreed as custom percentages or based on each buyer’s financial contributions. There is no legal requirement for one particular method, provided all owners agree and the ownership structure is documented appropriately.
Should ownership reflect the deposit?
It depends on the agreement between the buyers. Some co-buyers base ownership solely on deposit contributions, while others consider ongoing mortgage repayments and other costs as well.
Can I buy a house with friends in Australia?
Yes. Friends can purchase property together in Australia, although lenders will assess each borrower’s financial circumstances. Buyers should also seek legal advice regarding ownership structures and co-ownership agreements.
Can I buy property with my parents?
Yes. Many Australians purchase property with parents through co-buying arrangements, guarantor structures or other shared ownership arrangements. The most appropriate structure depends on individual circumstances.
What happens if one owner wants to sell?
The outcome depends on the legal agreement between the owners. A well-prepared co-ownership agreement can outline how valuations, buyouts and property sales will be managed if one party wishes to exit.
Does the calculator account for extra mortgage repayments?
Yes. If buyers collectively contribute more than the required mortgage repayment, the calculator can apply the surplus towards reducing the loan principal, allowing you to see how this affects future ownership and equity.
Does this calculator provide legal ownership advice?
No. The calculator provides financial modelling only. Ownership structures, legal title and co-ownership agreements should always be discussed with a solicitor or qualified legal adviser.
Is this calculator free?
Yes. The Fundd Co-Buying Calculator is free to use and is designed to help Australians better understand different approaches to sharing property ownership.
Make informed co-buying decisions
Buying property with other people can create opportunities that may not be possible alone, but agreeing on ownership from the beginning is just as important as choosing the property itself.
The Fundd Co-Buying Calculator allows you to compare different ownership approaches, understand each buyer’s financial contribution and estimate how future equity could be divided before making any commitments.
If you’re considering buying property with family, friends or another co-owner, the team at Fundd can help you understand your lending options and structure the purchase in a way that supports your long-term goals.
