Short answer. A full month, at least. Both formulas in Article 283 are written as one month's pay or a per-year amount, whichever is higher, so a worker with short service takes the one-month floor. Separation pay under this article never drops below one month.
What the law says
the separation pay shall be equivalent to one (1) month pay or at least one-half (1/2) month pay for every year of service, whichever is higher. A fraction of at least six (6) months shall be considered one (1) whole year.
Labor Code, Article 283 — Closure And Personnel Reduction. Read the full provision →
'Whichever is higher' is a floor, not a choice
This is the phrase people misread, and they misread it in the employer's favour. It does not mean the employer picks between two options. It means the entitlement is whichever of the two figures comes out larger — so the per-year computation only matters once it exceeds one month's pay. For a worker with a year and a few months behind him, it never will. The one-month figure is not a minimum grudgingly conceded at the end of the sum; it is the number the sum produces whenever service is short.
Working it through on short service
Take a retrenchment or a closure not due to serious business losses, where the rate is half a month's pay for every year of service. Fourteen months of service is one year, and half a month is plainly less than one month, so the entitlement is one month's pay. Now take redundancy or the installation of labour-saving devices, where the article sets one month's pay for every year of service. One year yields one month — the same figure. Either way the answer to your question is a whole month, not a fraction of one.
The rounding rule runs in your favour
The article adds that a fraction of at least six (6) months shall be considered one (1) whole year. So service is not counted in decimals. Nineteen months is two years, not 1.58; fourteen months is one year, the surplus two months simply falling away. On short service this rarely changes the outcome, because the one-month floor is doing the work regardless. It starts to matter once you are past the point where the per-year figure overtakes a month, and then a few months either side of the six-month line can move a whole year.
Which ground was invoked still matters
The half-month rate is expressly confined to retrenchment to prevent losses and to closures not due to serious business losses or financial reverses, so the ground written on your notice is not a formality. Get the notice in writing and see which of the article's grounds it names. Then check the pay base used against your payslips, because a computation applied to a bare basic rate when your pay regularly included more is the other place these figures go wrong. Take the notice, the computation and your payslips to a lawyer together.