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Using our Buy to Let calculator

Buy to Let calculator

See how much your customer could borrow with a Post Office Buy to Let mortgage.


Step 1 - ICR calculation

  • Enter the loan amount needed for this application, including any product fees to be added to the loan
  • Then enter the estimated or current monthly rental income
  • Choose either a 1-4 year or 5 year fixed term.  

Step 2 - Top Slicing calculation 

  • To see what your customer could borrow on a BTL Top Slicing mortgage, we need more information
  • Please expand each item below for more information on what you should and shouldn't include for our assessment:

Number of adults

Enter the number of applicants and any other adults who are financially dependent upon the applicants. All applicants must live at the same residential address and at least one must be a homeowner.

Number of children

Enter the number of children under the age of 18. Exclude any children who do not live with the applicants.

Annual income

If your customer is employed please include:

  • Their annual gross basic salary including any occupational pension (the amount before tax and national insurance deductions)
  • If the term requested will extend into the customer's retirement and their retirement is less than 10 years away, please include either their anticipated retirement income or their current income if lower
  • We’ll accept 50% of regular additional (non-guaranteed) income such as; overtime, commission and higher frequency bonuses
  • We won’t accept annual or bi-annual bonuses
  • Our underwriters may reduce the amount of reliance on this income at their discretion.

If your customer is self-employed, please average their last two years' earned UK taxable income (gross taxable income, not turnover), or use their most recent year's income if it’s lower than the average. Earned taxable income is defined as follows:

  • For sole traders, use their net profit figures
  • For partnerships, use their share of the net profit
  • For directors with a 25% or greater shareholding, use the total of their director's remuneration and dividend income.


If your customer receives child maintenance please include the annual amount received. The associated children should be entered in the “Number of children” field as financial dependants. Child maintenance cannot be the only form of income on an application.

If your customer receives foster income please average their last two years' earned UK taxable income, or use their most recent year's income if it’s lower than the average. Foster children must be included in the “Number of children” field as financial dependants.

Monthly outgoings

Enter the total amount (combined for joint applicants) your customer will continue to pay each month for committed outgoings. Details of what to include and exclude are listed below.


  • Car finance and personal loans
  • Student loans
  • Any loans or credit where acting as a guarantor
  • Second or subsequent charges secured on your customer's property
  • Hire purchase commitments
  • Overdraft interest calculated at 2% of the current overdraft balance
  • Credit card/store card/catalogue debts calculated at 3% of the current outstanding balance
  • Childcare costs/child maintenance/alimony
  • School fees
  • Interest costs on any non Buy to Let mortgages your customer holds calculated at 7.74% of the approximate balance at completion. But please don’t include their current residential mortgage.


  • Living expenses (e.g. food, utility bills, clothes, petrol)
  • Subscriptions to leisure activities (e.g. gym or golf club membership)
  • Pension contributions
  • Commitments, payments or rent that will cease if this mortgage completes
  • Monthly payments for other mortgages, even if they will continue after completion.

Residential mortgage details

If applicant 1 or 2 has an outstanding residential mortgage, please enter the outstanding balance and monthly repayment.

Existing Buy to Let properties

We need to make sure any Buy to Let borrowing is self financing or if not any shortfall will be classified as an outgoing.

Total balance of all Buy to Let properties (£) :

  • Enter the balance of all Buy to Let mortgages excluding this application. This must include any that are in joint names and all applications in progress
  • Please also include any that are in the name of a limited company which your customer is a director of.

Total monthly rental income (£) :

  • Enter the rental income achieved for all Buy to Let properties excluding this application
  • Please don't include any rental income already accounted for in your customer’s annual income.


Buy to Let calculator

See how much your customer could borrow with a Post Office Buy to Let mortgage.