From Monday there will be nearly 50,000 fewer Premium Bond winners each month as National Savings and Investments (NS&I) cuts to prize draws are rolled out.
The reduced chance of winning comes alongside cuts to NS&I savings rates, and will affect 21 million savers.
It is yet more bad news for savers, who have suffered from interest rates falling short of inflation, which currently stands at 2.3 per cent and is expected to go up in coming months.
The average easy-access savings rate has dropped 40 per cent in the past year, with the top 10 accounts offering on average just one per cent.
The new NS&I rates will apply to the Direct Isa, the Direct Saver and Income Bonds.
NS&I has said the move, announced in February, follows reductions in interest rates across the savings market, after the Bank of England base rate was cut to 0.25% in August.
Money held with NS&I is 100 per cent backed by the Treasury. NS&I has a duty to balance the needs of savers and taxpayers and help ensure the stability of the broader financial services sector.
The changes see a one per cent rate on NS&I's Direct Isa fall to 0.75 per cent, a 0.8 per cent rate on its Direct Saver fall to 0.7 per cent and a one per cent rate on Income Bonds fall to 0.75 per cent.
The estimated number of Premium Bond prizes in May will be 2,219,493, down from 2,268,165 in April's draw - a fall of 48,672.
The total Premium Bond prize fund value will fall from £70,880,100 in April to an estimated £63,810,400 in May. The reduced prize pot will see the estimated number of £100,000 prizes fall from three to two and there will be an estimated nine £25,000 prizes in May, compared with 13 in April.
Hannah Maundrell, editor in chief of money.co.uk, said: "If you've got a chunk of your money invested in NS&I Premium Bonds it really is time to start weighing up your options."
Premium bonds are seen as attractive in a time of low interest rates because of the possibility of a jackpot prize. But financial commentators have predicted that savers might choose to opt to put their money in the stock market instead amid low interest rates and increasing inflation.
When the new rates were announced, NS&I said the changes “reflect market conditions”. Earlier in April, NS&I launched a three-year investment bond with a rate of 2.2 per cent.
"We have taken the time to absorb the impact of the Bank of England base rate reduction and subsequent changes across the savings market," said Steve Owen, acting chief executive of NS&I, said at the time.
"The new rates reflect current market conditions and allow us to continue to strike a balance between the needs of our savers, taxpayers and the stability of the broader financial services sector.
"We appreciate that savers will be disappointed, but we believe that the new rates present a fair offer to customers."
Last month NS&I launched a three-year bond, which offers a rate of 2.2 per cent. Savers can put between £100 and £3,000 into the new Investment Guaranteed Growth Bond deal, which is on sale at nsandi.com for a 12-month period. Anyone over the age of 16 can apply.