The average rate being offered on a one-year fixed bond has fallen to a record low of 0.61%, according to a website.
Typical one-year bond rates are less than half the 1.28% average seen a year ago, Moneyfacts.co.uk said.
Six months ago, the average rate being offered on this product was 0.85%.
Rachel Springall, a finance expert at Moneyfacts, said the record low rate of 0.61% has been fuelled by rate cuts to several top deals, including those offered by challenger banks.
She said: “Thankfully, these brands continue to have a prominent presence in this area of the market, and the cuts are perhaps more linked to their attempts to cope with demand and realigning their position than deterring prospective investors completely.”
Looking across the savings market generally, there are now 1,517 savings deals including Isas on the market – 389 fewer than a year ago.
The average one-year fixed Isa rate stands at 0.58%, down by 0.63 percentage points over the past 12 months.
Ms Springall added: “It is crucial that savers review their existing Isa rate, especially if they had locked into a fixed deal that is due to mature.”