Martin Lewis is urging homeowners to check their mortgage deals - as they could save thousands of pounds a year.
This is because mortgage rates are currently pretty low, but are set to rise.
The price of mortgages partly reflects Bank of England base rate - currently 0.25%. That rose from 0.1% in December last year.
Mortgage lenders are passing this cost on, but very slowly, and fixed rate mortgages are still very cheap.
Mortgage prices are set to rise even further this year, as experts think the Bank of England will keep putting up base rate to help control soaring inflation .
MoneySavingExpert founder Lewis said: "Bank base rate increased to 0.25% in December, and with inflation rocketing, more rises are likely this year.
"Yet the rate of the cheapest new deals hasn't yet rocketed, so it's worth every mortgage holder checking now if they're on the best deal."
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Financial experts Moneyfacts said tracker mortgage prices - which as the name suggests, track base rate - have risen, from 3.38% in December to 3.53% this month.
That is a rise of exactly 15 basis points, matching the rise in base rate.
But the average two-year fixed deal increased from 2.34% in December 2021 to 2.38% in January 2022 - just 4 basis points.
The typical five-year fixed rate loan rose from 2.64% in December 2021 to 2.66% in January 2022, or 2 basis points.
So it's a good time to consider a fixed-term loan, but an even better time for first-time buyers.
Moneyfacts said the average two and five-year fixed-rate mortgage rates for borrowers with 5% deposits are actually falling - and have been for nine months in a row.
These are 3.06% and 3.33% respectively, the lowest on record.
But all this means homeowners able to remortgage now can lock in to a cheap fixed rate deal before prices start rising in earnest.
You don't need to be right at the end of a mortgage term to take advantage of this.
Most mortgage lenders will let you take out a new loan six months before your current one ends.
Why are mortgage rates so low?
The Bank of England base rate has actually been low since 2020 - but lenders did not pass any of that on until 2021.
When they did, mortgage rates fell to record lows.
There are several reasons why homeloans suddenly became so cheap.
Firstly lenders may have been worried about their own profits during the worst of the coronavirus outbreak, and not feeling particularly generous.
But experts also think mortgage lenders are being super-competitive with lower-deposit mortgages to balance out the rush of riskier first-time buyer mortgages.
Banks see first-time buyers as much more likely to default on mortgages, as they tend to borrow higher amounts.
Not only that but they are often younger and less established in their careers.
There were a lot of first-time buyers last year because in April the government launched Treasury-backed 95% mortgages.
Under the government guarantee scheme, banks and building societies offer mortgages to borrowers with just a 5% deposit, with the government acting as the guarantor if the buyer defaults on their payments.
Fixed-rate mortgage prices are also heavily affected by swap rates - the rate at which mortgage lenders borrow money from one another.
When swap rates fall, so do fixed-rate mortgages. It's not an exact system, but it's a good rule of thumb.
As swap rates have been so low for most of 2020 and 2021, fixed-rate loans fell too.
