Here are my workings. Welcome comments or thoughts. Based on these I believe that there are savings in cash terms of about 6 grand (285,612 less 279,993 = 5,619) over the ten year period. Many different configurations can be made, eg interest only for one year, etc. Also tables below are a summary for the ten years, just as easy to do one per year though would take time.
Existing positions - assume both mortgages are being paid on a full capital and annuity basis
Three columns - PPR/ Inv Prop/ Total
Mortgage balance - 120,000/ 135,000/ 255,000
Interest rate - 1.35%/ 5.00%/na
Period left (years) 10 years each
Estimates only
Monthly repayment - 1,070/ 1,430/ 2,500
Total gross repayments (10 years) - 128,400 / 171,600 / 300,000
Includes interest of: - 8,400 / 36,893 / 45,293
Net interest
(assume marginal tax 52%, 75% int deduction**) - 8,400 * / 22,505** / 30,905
Saving' due to tax relief on interest on Inv Prop - na / 14,388 / 14,388
Total net repayments (10 years) (out of pocket) - 128,400 / 157,212 / 285,612 (this is the total cash payments to be made under existing situations, ie two annuity mortgages being paid in full over ten years)
* No difference, not tax deductible
** Assume relief for interest available, ie receiving rent and in a position to avail of interest deduction. Calculated as (36,893 less 75% of 36,893 tax relieved at 52%)
Revised position - assume PPR interest only until Inv property paid off. Thereafter the PPR is paid off within the original ten year period also
Three Columns - PPR / Inv Prop / Total
Mortgage balance - 120,000 / 135,000 / 255,000
Interest rate - 1.35% / 5.00%/ na
Period left (years)- 10 years each
Estimates only
Monthly payments initially (first 5 1/2 years) - 135 / 2,365 / 2,500 NOTE 1 NOTE 2
Monthly payments when Inv Prop fully paid (i.e. After 5 1/2 years) - 2,300/ Zero (fully repaid) / 2,300
Total gross repayments (over the ten year period) - 133,110 / 154,480 / 287,590 NOTE 3
Effect of tax deduction of interest on Inv Prop - na / 7,597 (Note 4)
Total net repayments (10 years) (out of pocket) - 133,110 / 146,883 / 279,993
NOTE 1 - PPR on interest only at 1.35% pa would require a monthly payment of €135 to meet interest cost. Assume the balance of the monthly payment of €2,500 under the existing situation is then all used to pay the investment property until it is paid off.
NOTE 2 - Investment property paid off in full by month 66 (i.e. 5 and a half years). From that point onwards assume that the payment is made to the PPR to allow it to be fully cleared by end of year 10. To facilitate this the monthly payment should be approx €2,365.
NOTE 3 - Comprises €135 per month for 5 1/2 years and €2,300 per month for the remaining 4 1/2 years, such that the PPR mortgage is fully repaid within the ten year period
NOTE 4 - Interest cost is 154,480 less mortgage 135,000 = 19,480. Tax relieved at 19,480 *75% *52% = 7,597