The most common and most likely answer to this crossword clue is the 6 letter word ABACUS
I've seen this crossword clue in The Daily Telegraph
A
B
A
C
U
S
More clues leading to the result ABACUS
- A church removed from god, you can count on it!
- A taxi brought over American? One may count on it
- An American possessing endless support you can count on?
- Copper in a station endlessly? You could count on this once
- Primarily adjusting beads, apparatus Chinese use still?
- Copper's after a degree: you can count on it!
- Grab a customer pinching calculator
- Cooling system in a vehicle that’s helpful for summer?
- A church abandoning God for something they can count on
- Old calculator that may make a graduate swear endlessly
Buddy explains!

The straight part
We know that "Early summer, one could count on it" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case early summer, one could count on it = abacus.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does ABACUS mean?
ABACUS noun- A table or tray scattered with sand which was used for calculating or drawing.
- A device used for performing arithmetical calculations; a table on which loose counters are placed, or (more commonly) an instrument with beads sliding on rods, or counters in grooves, with one row of beads or counters representing units, the next tens, etc.
- The uppermost portion of the capital of a column immediately under the architrave, in some cases a flat oblong or square slab, in others more decorated.
- A board, tray, or table, divided into perforated compartments for holding bottles, cups, or the like; a kind of buffet, cupboard, or sideboard.