On a typical £115,000 mortgage lasting 25 years, monthly repayments are now £732 per month. If base rates rise to 5%, it would cost an extra £18 per month, or £216 a year. If they go up to 5.25%, monthly repayments will be £36 higher, an annual rise of £432. But if base rates soar to 5.5%, monthly repayments will be £54 higher, a hefty £648 extra a year.