Since or For? Duration in OET Patient History

Since or for isn’t a coin-flip choice in OET writing — it’s a binary grammatical test that case notes force on you every time a patient history reports how long a symptom, medication, or condition has lasted. Get it backwards and the sentence doesn’t just sound slightly off to an examiner marking against the Language criterion; in a lot of cases it stops being grammatical English at all. “She has had back pain since three weeks” is not a minor stylistic slip. It’s a construction error, and it’s one of the most common Language-criterion losses in OET writing because the underlying information — duration — comes up in nearly every letter you’ll ever write.

Watch the full breakdown: Since or For? Duration in Patient History works through this exact decision using real case-note duration phrases.

Why does this one preposition choice matter so much in OET writing?

Duration is one of the most frequent pieces of information a patient history has to carry. Almost every referral, discharge, or transfer letter needs to tell the receiving clinician how long a symptom has been present, how long a patient has been on a medication, or how long they’ve been waiting for a procedure. Case notes hand you that duration in a raw, compressed form — “3/7 cough,” “on metformin x 3 yrs,” “started Monday” — and you have to convert it into a correctly built English sentence before the letter can do its job. Since and for are the two words that carry almost all of that conversion work, which means getting the choice wrong isn’t a rare edge case. It’s a recurring opportunity to lose Language marks across the entire letter, not just in one sentence.

This also sits squarely inside the Content criterion, not only Language. If a receiving GP reads “since two weeks” — a construction that doesn’t parse cleanly — they lose a beat working out whether you meant a two-week duration or a specific day two weeks ago. A letter that makes its reader stop and reinterpret a sentence has already failed at the one job a referral letter has: getting information across cleanly, the first time, with nothing to double-check.

Since or for: the two-word test for duration in OET writing

The decision comes down to what kind of time expression follows the word, and it’s a mechanical test once you see it laid out:

Once you can categorise the time expression itself — point or span — the choice of since or for follows automatically. The error almost never comes from not knowing the rule. It comes from not pausing to run the test before writing the sentence, especially when you’re converting shorthand case notes into prose under time pressure.

Since: a starting point, not a length

Since always attaches to a point on the timeline — the moment something began — never to a quantity of time. That point can be a day of the week, a calendar date, or a named clinical event:

“She has experienced intermittent palpitations since Thursday.”

“He has reported reduced appetite since his chemotherapy began.”

“The wound has remained unhealed since the initial dressing change.”

In each case, since is doing one job: marking the exact moment the present-perfect situation started. Everything after since must be a point, not a span — “since Thursday” works because Thursday is a specific day; “since three days” does not work, because three days is a length, and that’s exactly the error for is built to handle.

For: a length of time, not a point

For attaches to a span — a quantity of time with no fixed calendar point named — and it’s just as rigid about staying on its own side of the rule:

“He has taken warfarin for approximately eighteen months.”

“She has reported lower back pain for two weeks.”

“The patient has used a walking frame for the past six months.”

Notice that “the past six months” still counts as a span, even though it contains the word “past” — it tells you a length (six months), not a point on the calendar. This is the detail that trips candidates who assume any phrase containing a specific-sounding word must take since. The test stays the same regardless: point takes since, span takes for.

Where this goes wrong: swapping the two mid-sentence

The most common version of this error isn’t choosing the wrong tense — it’s attaching the right present-perfect verb to the wrong preposition, which produces a sentence that fails grammatically rather than just reading awkwardly:

Incorrect: “She has had nausea since two days.”

Correct: “She has had nausea for two days.”

Incorrect: “He has been on dialysis for his transplant referral.”

Correct: “He has been on dialysis since his transplant referral.”

The first pair swaps a span (“two days”) onto since, which doesn’t accept spans at all — the sentence is not valid English, not merely informal. The second pair swaps a point (“his transplant referral”) onto for, which doesn’t accept points. Both errors are more serious than they look, because an examiner marking against the Language criterion isn’t deducting for style here — they’re reading a sentence that a native-level writer would never produce, which signals a gap in basic grammatical control rather than a surface slip.

Since, for, and the present perfect they both depend on

Since and for both normally pair with present perfect, because the entire reason you reach for either word is that the duration you’re describing is still ongoing at the moment you’re writing the letter — the symptom hasn’t resolved, the medication hasn’t stopped, the wait hasn’t ended. That’s a related but separate decision from the since/for choice itself: our past simple vs present perfect guide covers how to decide whether an event is closed (past simple) or still open (present perfect) in the first place. Since/for choice only comes into play once you’ve already established that the duration is open — it decides which of the two prepositions correctly names the specific point or span you’re attaching to that open duration. Getting the tense right and the preposition wrong, or the reverse, are both live possibilities in the same sentence, which is why it’s worth treating them as two separate checks rather than one.

A quick self-check before you submit

Run this two-step test on every sentence in your patient history that reports how long something has lasted:

1. Identify the time expression. Is it a point (a day, date, or named event) or a span (a length of time, with or without “the past”)?
2. Match the word to the type. Point takes since. Span takes for. If the sentence doesn’t fit either category cleanly, rewrite the time expression itself before worrying about which preposition to use.

This check is quick to run because it’s purely mechanical once you isolate the time expression — the hard part is remembering to isolate it at all, rather than reaching for whichever word feels more natural in the moment. Pulling every duration phrase in your letter into a short list before you finalise your draft, exactly the way you’d check for subject-verb agreement in longer clinical noun phrases, catches this error reliably where a normal read-through tends to miss it, because since and for both sound fluent even when they’re attached to the wrong kind of time expression.

Duration phrases like these come straight out of the case notes, so the accuracy of this check depends on reading the source material carefully in the first place — our guide to reading OET case notes covers how to pull timing information out of abbreviated case notes without losing precision. If you want a broader pass across all of the Language criterion’s component skills, our Language criterion video lesson walks through grammatical range and accuracy together, since/for sitting alongside tense and article choice as one of the recurring error types examiners mark against.

The honest limit of self-editing here

Since and for both sound completely fluent to the writer who produces them, because the error isn’t in how the sentence reads out loud — it’s in whether the word matches the kind of time expression attached to it, a mismatch that’s easy to miss when you’re focused on content rather than grammar. The free OET Grammar Checker catches a useful first pass of surface grammar errors, though a since/for mismatch buried inside an otherwise fluent sentence is exactly the kind of error that benefits from a second, trained reader checking your letter line by line. Our OET writing correction service has corrected 11,000+ letters since 2014 and reviews your letter against all six official criteria — including the duration-marking errors that read as fluent English to the person who wrote them and as a Language-criterion loss to the examiner marking it.