since (for) + 'period of time'

Use since to name a starting point (a date, day, event). Use for to name a duration (how long).

Below: a quick rule, concise checks, many copyable wrong/right pairs, rewrites for work/school/casual sentences, and near-miss expressions to watch.

Quick answer

Since = start point (since March, since 2015, since the accident). For = duration (for three days, for ten years, for a long time). If the phrase answers "When did it start?" use since. If it answers "How long?" use for.

Since → a specific start (date, year, day, event).
For → length of time (hours, days, months, years, indefinite spans).
If you can replace the phrase with a date, use since; if you can replace it with "three years" or "two weeks", use for.

Core explanation: short and practical

Since points to when something began and usually appears with perfect tenses when the action continues now. For measures how long something lasted or has lasted.

Model: I have lived here since 2012. (start) / I have lived here for eight years. (length)

Since → since + point in time (year, date, day, event).
For → for + duration (numbers + units, "a long time", "a while").

Grammar quick rules (tenses and structure)

Since often pairs with present perfect or present perfect continuous because those tenses describe actions that started in the past and continue: I have known her since 2010; I've been waiting since noon.

For appears with any tense that communicates duration: I waited for two hours; I've worked here for five years; He lived abroad for a year.

Present perfect + since = start point: She has studied here since 2017.
Present perfect + for = duration: She has studied here for three years.
If you see "since" followed by a number (since two years), swap it for "for" and usually write numbers as words in formal text.

Wrong: I've known him since ten years.
Right: I've known him for ten years.
Wrong: They have been on strike for 2019.
Right: They have been on strike since 2019.

Spacing and punctuation: small but common typos

Keep a single space between the preposition and the time phrase. Use a comma after a long introductory time phrase: For the first three months, we worked remotely.

Wrong spacing: since2018 → Correct: since 2018.
Use a comma for long introductory phrases: For two weeks, the system will be down.
Avoid double spaces between words; they look like mistakes.

Wrong: I've been here since2018.
Right: I've been here since 2018.
Wrong: For2 years, we tested the prototype.
Right: For two years, we tested the prototype.

Hyphenation and compound modifiers: when to hyphenate

You don't hyphenate since/for with their time phrase. Hyphens appear when a duration becomes a compound adjective before a noun.

Correct adjective: a three-year plan (hyphen because it modifies "plan").
Incorrect: for-three-years contract →
Correct: a three-year contract.
Correct sentence use: We've been partners for three years. (no hyphen)

Wrong: We've had a for-three-years contract.
Right: We've had a three-year contract.
Wrong: He is since-2010 with the firm.
Right: He has been with the firm since 2010.

Real usage and tone: formal vs casual choices

Use since when the exact start matters. Use for when the listener cares about length. Casual speech often shortens phrasing, but don't swap the prepositions.

Start-focused (since): The program has run since 2004.
Duration-focused (for): The program ran for three years.
Speech often drops small words: "I've had this job five years." - understood as "for five years", never "since five years".

Usage: Formal: The policy has been active since January 1, 2020.
Casual: It's been active for three years.
Usage: Start emphasis: She has driven the route since last summer. Duration emphasis: She drove the route for two months.

Try your own sentence

Test the whole sentence rather than the phrase by itself - context usually makes the right choice clear.

Examples you can copy - many wrong/right pairs (work, school, casual)

Each pair shows a common learner error (wrong) and the corrected version (right). Copy the right sentence and adapt the time expression as needed.

Work, school and casual templates below are ready to paste into emails, reports, essays and messages.
When you fix something, usually only the preposition changes; sometimes the noun phrase needs editing (e.g., "three semesters" not "three semester").

Work:
Wrong: I've been managing this account since six months.
Right: I've been managing this account for six months.
Work:
Wrong: She has been at the company since two years.
Right: She has been at the company for two years.
Work:
Wrong: We've been using that vendor since three quarters.
Right: We've been using that vendor for three quarters.
Work:
Wrong: The project ran since April to July.
Right: The project ran from April to July. / The project ran for three months.
School:
Wrong: I've studied biology since three semesters.
Right: I've studied biology for three semesters.
School:
Wrong: She has practiced piano since two hours.
Right: She has practiced piano for two hours.
School:
Wrong: They have lived on campus since four years.
Right: They have lived on campus for four years.
School:
Wrong: I attended the course since 2015 (meaning: during 2015).
Right: I attended the course in 2015. / I attended the course during 2015.
Casual:
Wrong: We've known each other since ten years.
Right: We've known each other for ten years.
Casual:
Wrong: I've had this phone since a long time.
Right: I've had this phone for a long time.
Casual:
Wrong: I've been tired since weeks.
Right: I've been tired for weeks.
Casual:
Wrong: I met her since two years ago.
Right: I met her two years ago.

Rewrite help: quick fixes you can paste

When you see "since" + duration or "for" + date, swap the preposition and adjust the phrase. Below are original sentences and clean rewrites.

Swap only the preposition when that's all that's wrong. If the time phrase itself is wrong, fix both.
Choose "ago" or "during" when they match the meaning better than since/for.

Rewrite:
Wrong: I have been working here since 2 years.
Rewrite: I've been working here for two years. Why: "since" needs a start point.
Rewrite:
Wrong: The club has existed for 1999.
Rewrite: The club has existed since 1999. Why: "since" pairs with a start date.
Rewrite:
Wrong: He's been sick since a long time.
Rewrite: He's been sick for a long time. Why: "a long time" is a duration.
Rewrite:
Wrong: We lived here since 2010 to 2015.
Rewrite: We lived here from 2010 to 2015. / We lived here for five years. Why: Ranges use "from...to" or a duration with "for".
Rewrite:
Wrong: She has trained since six months as a TA.
Rewrite: She has trained for six months as a TA. Why: "six months" is a duration.
Rewrite:
Wrong: The course ran since last fall.
Rewrite: The course ran from last fall. / The course ran last fall. Why: If it ended, avoid "since".

Memory tricks and quick checks

Two quick mental checks stop most errors.

Ask "When did it start?" - if you can answer with a date or a point (2016, Monday, graduation), use since.
Ask "How long has it lasted?" - if you can answer with a span (two years, three hours, a while), use for.
Replace the phrase with "since 2019" or "for three years" - whichever sounds natural is probably correct.

Check: Replace "since he moved" with "since 2019" or "for three years" to see which fits the meaning.

Similar mistakes to watch for

Learners mix since with ago, for with during, and since with from/in. Each expression has a different function - examples below show correct usage.

Since vs. ago: Since names a start point that continues to now; ago places an event in the past. Correct: "I met her two years ago." Not: "I met her since two years ago."
For vs. during: For = duration; during = inside a period. Use "during the meeting" (inside that time), not "for the meeting" unless you mean the length.
Since vs. from/in: Since = start point tied to the present; from often needs an end point: from May to August.

Wrong: I met her since two years ago.
Right: I met her two years ago.
Wrong: I learned French since high school (meaning: during high school).
Right: I learned French during high school.
Wrong: The conference ran since Monday to Wednesday.
Right: The conference ran from Monday to Wednesday.
Wrong: We lived here since 1998 until 2002.
Right: We lived here from 1998 to 2002.

FAQ

Can I use since with numbers like "since two years"?

No. Use "for" with numeric durations: "for two years." Use "since" with a clear start point: "since 2019", "since Monday", "since graduation."

Is "since last week" correct?

Yes, when something started last week and continues now: "I've been busy since last week." If you mean "throughout last week," use "during last week."

Which is correct: "I've been here since 3 years" or "for 3 years"?

Correct: "I've been here for 3 years." Use "for" for durations measured in units (years, months, hours).

When should I use "from" instead of "since"?

Use "from" when you specify both a start and an end or describe a range: "from May to July." Use "since" when you give only the start and the action continues into the present.

Can "since" and "for" appear in the same sentence?

Yes. Example: "She has lived here since 2010 and has taught at the school for nine years." Each preposition serves a different function (start vs duration).

Want a quick check?

If you're unsure, paste the sentence into a grammar tool or swap the phrase with "since 2019" and "for three years" to see which meaning you intend.

Save a few corrected templates from the examples above and reuse them in emails, reports, and posts until choosing feels automatic.