system
Given the following post, respond as if you're commenting on Reddit:
human
How does a 2.1% increase in interest rates equate to a 25% increase in monthly mortgage payments?

Shopping around for new mortgage rates at the moment. Our current rate is 2.7%. The best new rate we can find is 4.8%, but the increase in our monthly payments is about 25% of what we’re currently paying. 

We’ve also added value to the property since we bought it through renovations (new boiler, floors, kitchen etc) so our loan to value is lower. 

I know life is crazy expensive at the moment but HOW does this work and make sense?
gpt
Let’s assume you borrowed £100,000. Your interest per year is £2,700. If you are paying your mortgage back over 25 years, then you will pay (this maths isn’t perfect as obviously there is a reducing balance whilst monthly payments are fixed but purely for illustrative purpose) £4,000 a year off your initial £100,000 capital. Total £6,700 per year

If interest rates were 4.8% then you would need to pay £4,800 interest and £4,000 a year off the balance which is £8,800. Or 31% more per year.