Grading baseball cards is sold as an upgrade and is better understood as a purchase. You are buying certainty about condition, and the card has to be worth enough more with that certainty than without it to cover what you paid. Most cards are not, and the arithmetic that shows which are is short.
What you get for the money
A grader examines the card against a published scale, assigns a number, seals it in a tamper-evident holder and records a certification number that anyone can look up. The buyer no longer has to trust a photograph or a seller's adjective about corners. That is a real service and it is priced accordingly, per card, with the postage on top.
The three cards worth sending
In practice a card justifies grading when it is scarce enough that condition swings its price a long way, sharp enough that a high grade is plausible, and liquid enough that a graded example will actually sell. Fail any one of the three and the submission usually loses money: a common card graded highly is still common, and a scarce card graded poorly is a scarce card with its flaws now certified.
Cost it before you post it
Put the per-card fee, the extras, the outbound postage and the insured return into the grading cost calculator and read the cost per card. That number is the hurdle. Then put the raw price, the price at the grade you honestly expect and that cost into the uplift calculator, and the answer is a single figure with a sign in front of it.
Grade expectation is where people go wrong
Use the price for the grade you will probably get. Almost everybody guesses a grade above where their card lands, and because the steps between grades are irregular and the top step is often most of the money, a one-grade miss can turn a comfortable profit into a loss. Being pessimistic here costs nothing and saves submissions.
Questions people ask about grading baseball cards
Should I grade a whole box of cards?
Almost never. Cost the cards individually against the per-card figure and you will usually find that a handful clear the hurdle and the rest are worth more raw, because the fee is the same whatever the card turns out to be worth.
Does grading protect the card?
The holder protects it physically, which is a genuine benefit if you are storing or shipping. That is a different question from whether it adds value, and it is worth separating the two when you decide.
Which grader should I use?
This site does not rank graders and takes no money from any of them. What matters for the arithmetic is which grader's slabs the buyers for your particular card actually pay for, and that shows up in completed sales.
Can I submit directly or do I need a dealer?
Graders generally accept direct submissions, sometimes with a membership. Going through a dealer or a submission centre can share the postage across more cards, which is a real saving and a question of trust.