The option of three-month payment holidays was introduced by the government to help borrowers impacted by the coronavirus pandemic.
Lenders have been keen to support the initiative, but many have been overcome by the levels of enquiries from customers.
The adviser firm said it wanted to remind those considering a mortgage holiday that while they are not making your mortgage payments, the interest is still building up; and, when the holiday is over, your mortgage balance and payments will be higher.
Its calculation will give people an illustration of how much their balance will increase by and how it is likely to affect monthly payments.
To use the calculator, borrowers will need their initial mortgage value, mortgage rate, mortgage term, date the mortgage was taken out and length of the mortgage holiday.
Online Mortgage Advisor managing director Pete Mugleston said borrowers should get in touch with their lender if they think they may need support.
He added that mortgage holidays are usually only recommended as a last resort and potential alternatives should be considered.