Table:
|  | Year Ended |  |  |
| --- | --- | --- | --- |
|  | December 27, 2019 | December 28, 2018 | December 29, 2017 |
| Weighted average expected term | 0.5 years | 0.5 years | 0.4 years |
| Risk-free interest rate | 2.3% | 1.9% | 1.1% |
| Dividend yield | 0.0% | 0.0% | 0.0% |
| Volatility | 56.0% | 52.7% | 47.8% |
Paragraphs:
2017 ESPP
In May 2017, we adopted the 2017 Employee Stock Purchase Plan (the “2017 ESPP”). The 2017 ESPP grants employees the ability to designate a portion of their base-pay to purchase ordinary shares at a price equal to 85% of the fair market value of our ordinary shares on the first or last day of each 6 month purchase period. Purchase periods begin on January 1 or July 1 and end on June 30 or December 31, or the next business day if such date is not a business day. Shares are purchased on the last day of the purchase period.
The table below sets forth the weighted average assumptions used to measure the fair value of 2017 ESPP rights:
We recognize share-based compensation expense associated with the 2017 ESPP over the duration of the purchase period. We recognized$0.3 million, $0.3 million, and $0.1 million of share-based compensation expense associated with the 2017 ESPP during 2019, 2018, and 2017, respectively. At December 27, 2019, there was no unrecognized share-based compensation expense.
Question:
When do the purchase periods begin?
Answer: January 1 or July 1