OVERDOSE
Human Experience
Of 1,027 cases of overdose involving sertraline hydrochloride worldwide, alone or with other drugs, there were 72 deaths (circa 1999).
Among 634 overdoses in which sertraline hydrochloride was the only drug ingested, 8 resulted in fatal outcome, 75 completely recovered, and 27 patients experienced partial recovery with lasting effects. The remaining 524 cases had an unknown outcome.
The largest known ingestion was 13.5 grams in a patient who took sertraline hydrochloride alone and subsequently recovered. However, another patient who took 2.5 grams of sertraline hydrochloride alone experienced a fatal outcome.
Source: http://www.rxlist.com/zoloft-drug/overdosage-contraindications.htm
These are pretty bad stats if it is your only choice of pills. And the answer for doses is always; ALL the pills.