The Maths: Why Savings Usually Win Over Borrowing
The core arithmetic is straightforward. If your savings account earns 4.5% per year and a secured loan charges 9% APR, you are paying a net 4.5% per year on any amount you could have funded from savings but chose not to. On a £20,000 home improvement over five years, this net cost is approximately £4,700 in unnecessary interest — money you are paying the lender that you did not need to borrow at all.
This calculation becomes even more favourable for savings when you consider that savings interest is received on the declining balance of your savings as they grow (if you leave them untouched), while loan interest is charged on the declining balance of the loan as you repay it. The exact arithmetic depends on the timing, but the principle is consistent: any money you borrow that you could have used from savings costs you the difference between the savings rate and the loan rate for the duration you hold both positions.
The calculation reverses when the improvement itself generates a return. A kitchen extension that adds £30,000 to a property value in two years generates a return in excess of most borrowing costs, making borrowing to fund it financially rational — you get the value uplift with only the loan amount at risk, rather than deploying your own capital that could be earning a return elsewhere. If your savings are invested in assets earning more than the loan rate — ISAs, stocks and shares, or pension contributions receiving employer matching — the case for keeping savings invested and borrowing for the improvement is stronger.
In the current environment (2025), cash savings in easy-access accounts are earning 4% to 5%, fixed-term accounts somewhat more, and ISAs within similar ranges. Secured loan rates for most homeowners range from 7% to 14% APR. The spread — the cost of borrowing minus the savings return — is typically 3% to 8%. This means using savings for home improvements is usually the cheaper option, and borrowing should be justified by specific reasons rather than chosen as the default.
The Emergency Fund Argument: When Keeping Savings Makes Sense
Financial planning guidance consistently recommends holding three to six months of essential living costs in accessible savings — the emergency fund. This buffer is designed to cover unexpected income loss (redundancy, illness, or other employment disruption) or large unplanned expenses without needing to borrow at short notice. Depleting the emergency fund to fund a home improvement leaves you exposed: if something goes wrong immediately after the improvement, you have no buffer and would need to borrow, potentially at a higher rate than the secured loan you avoided, and potentially at a difficult time when credit is less available.
For most households, the practical answer is not to choose entirely between savings and borrowing, but to find a sensible balance. Using half your available savings and borrowing the remainder, for example, depletes some savings (reducing the borrowing cost) while preserving a meaningful buffer (maintaining the emergency fund purpose). This hybrid approach is not mathematically optimal, but it is practically sensible for most real-world households with competing financial priorities.
The emergency fund argument is strongest for households where income is less predictable — self-employed borrowers, those on variable or commission-based pay, or households where both earners are in the same industry and therefore face correlated income risk. It is weakest for households with stable public sector or professional employment, strong existing financial resilience, and the ability to quickly rebuild savings after the improvement from ongoing income.
Another consideration is psychological: many people feel significantly more financially secure knowing they have savings available, even if the mathematically optimal approach would say to use them. The peace of mind value of liquidity is real, even if it does not appear in a rate comparison. There is nothing irrational about choosing to borrow some of the improvement cost to preserve a savings buffer that makes you and your household feel more financially secure.
