“I was not in a good place. Every day not seeing a therapist felt much more urgent,” says Ms. Pratt.

Especially in big cities such as Los Angeles, New York and Washington, D.C., demand for mental-health care is so strong that many experienced therapists don’t accept any insurance plans, they say. They can easily fill their practices with patients who would pay out of pocket, they add. Therapists who do take insurance are often booked up. And in many smaller towns and rural areas, there are few mental-health professionals at all. Finding a provider who takes insurance, or lowering your rates in other ways, is possible but often takes legwork that can be draining when you are already grappling with mental-health issues.

Paying out of pocket for individual weekly therapy can add up to thousands of dollars a year. In major cities, the going rate for experienced clinical psychologists can be as much as $300 for a 45-minute session. The typical fee for a session with a licensed clinical social worker is between $120 and $180, says Anna Mangum, deputy director of programs at the National Association of Social Workers. Patients with out-of-network benefits may be able to receive reimbursement for a portion of the bills. But using in-network providers often means patients only have to pay a small copay.

Psychologists, social workers and psychiatrists who don’t accept insurance say that insurers’ reimbursement rates are too low. Ms. Mangum says insurance companies commonly pay social workers about one-third to one-half the fee they can charge out of pocket. Some therapists also complain about the paperwork and restrictions on the kinds of care that are covered.

“If you’re good enough and have good enough marketing and are in demand, then it’s just a financial decision” to not take insurance, says Ken Goodman, a licensed clinical social worker in Los Angeles and board member of the Anxiety & Depression Association of America. Mr. Goodman says he dropped his last insurance provider about a year ago. “I make twice as much if I just accept cash.”

Hurdles to Finding a Therapist

About 34% of people with private insurance said they had difficulty finding a therapist who would accept their coverage, according to a 2016 survey—the most recent data available—of more than 3,100 participants conducted by the National Alliance on Mental Illness, a national mental-health advocacy group. By comparison, 9% said they had difficulty finding an in-network primary-care provider.

Office visits to mental-health providers are more than five times more likely to be out of network than are visits to primary-care providers, according to a 2019 report from Milliman, a consulting firm, which analyzed insurance-claims data. In 2017, 17.2% of mental-health office visits were out of network, compared with 3.2% of primary-care visits, the Milliman report found.

Many psychologists accept insurance early in their careers while they are building their practices, but some reduce or drop it as they gain experience and word-of-mouth referrals, says Lynn Bufka, a clinical psychologist and senior director at the American Psychological Association. About 55% of psychiatrists accepted private health insurance in 2009-2010, according to a study published in 2014 in JAMA Psychiatry that used data collected by the Centers for Disease Control and Prevention. About 89% of physicians in other specialties accepted private insurance. Because of low reimbursement rates and administrative issues, the numbers for psychiatrists probably haven’t changed much since, says

Saul Levin,

chief executive and medical director of the American Psychiatric Association.

What Patients Can Do

If you can’t find a therapist in your area who takes your insurance, has availability and can adequately treat your condition, you might be able to arrange what is known as a single case agreement between an out-of-network provider and your insurance company.

Aarti Gupta, a clinical psychologist in Palo Alto, Calif., says she has negotiated these agreements for a few patients, including for a teenager with suicidal thoughts and for ones with rarer conditions, like trichotillomania, a hair-pulling disorder. Dr. Gupta stopped taking insurance plans in 2017, about a year after opening her own private practice.

Telehealth can provide access to a broader pool of providers, including therapists who are farther away from you.

And some therapists who don’t take insurance have a sliding scale. Dr. Gupta, for example, reserves two lower-priced slots in her schedule. And, of course, make sure you are submitting for any out-of-network benefits you are entitled to.

What Insurers Are Doing About It

Insurance companies say they are trying to increase access to therapists.

Anthem Inc.

says it added about 2,000 additional providers to its telehealth platform during the early days of the pandemic to handle increased demand.

UnitedHealth Group Inc.

says it has grown its network of mental-health-care providers by 50% in the past five years to more than 260,000 nationwide.

As for therapists’ complaints of low reimbursement rates, Anthem health plans “routinely review reimbursements to ensure that providers receive market rates,” the company said in a statement. Margaret-Mary Wilson, UnitedHealth Group’s associate chief medical officer, says the company uses data on how patients are improving to financially “reward providers for delivering care with better outcomes.”

Success, With Legwork

Ms. Pratt, the teacher in Boston, did eventually find a therapist who took her insurance. She says she was again on the hunt for an in-network therapist this summer after hers retired.

She says she sent a detailed email to 20 therapists; 16 never replied. Two wrote back to say they weren’t taking new patients. But two had space. Ms. Pratt says she chose one and has seen her new therapist twice now. She says the legwork was worth it. For each session, she owes just a $20 copay.

Write to Andrea Petersen at andrea.petersen@wsj.com