Right now, pensioners who visit council run day centres get the service for free. But from April 1, they will have to pay up to £15 a day.
Social work bosses say the charges are necessary as other groups, including people with physical or learning disabilities, are already billed for day care.
A letter has gone out to around 2000 people who will be affected.
Single people who have a weekly income of less than £173 a week after rent, council tax and other bills such as community alarm payments will not be charged.
Couples with a weekly income of less than £264 a week after bills will also be allowed to attend day care centres for free.
Everyone else will be charged according to their income up to a maximum of £15 a day.
The actual cost of day care services for elderly people in Glasgow is almost £40 a day.
Elderly people will have to fill in a financial assessment form to allow the council to determine whether or not they will be charged and if so, how much.
It is expected around half of those who attend day centres will continue to do so for free.
Council bosses insist charges are necessary if they are to avoid the threat of a legal c hallenge from other groups who already pay for day care.
The letter says: "In Glasgow, all adult service users of social work services between the age of 18 and 65 currently undergo a financial assessment to see if they can afford to make a payment towards the cost of their social care support.
"As a result of the Social Care (Self-Directred Support) (Scotland) Act 2013, which comes into force in April this year, the council must now use the same system for financial contributions for older people over the age of 65.
"This is to make sure all people over 18 years who use social care services are treated in exactly the same way and that there is consistency and fairness across the whole social work system for adults in Glasgow."
It is understood nine councils across Scotland already charge for the elderly including Dundee, which has a rate of £35.46 a day and South Lanarkshire, which charges £34.98.
A Glasgow spokesman said: "We fully accept that people will not be happy about this, but the effect of new social care legislation is that we have to charge for day care services.
"Asking people to make a contribution to the cost of their day care services is about being consistent and fair to other social work service users.
"If other care groups are asked to contribute financially for certain care services, it cannot be fair that one care group is treated any differently.
"It must also be stressed that those who cannot afford to pay will not be expected to pay.
"Many other local authorities already charge for day care service and a significant majority of the cost of the Glasgow service will continue to be picked up by the council.
"All service users will be written to and asked to complete a financial assessment form so that we can directly link the amount someone contributes to their ability to pay."