Before I turn to our key first quarter operational achievements, I want to note that working with the Greg Hill Foundation, our Sam Adams Restaurant Strong Fund has raised over $7.5 million dollars thus far to support bar and restaurant workers who were experiencing hardships in wake over COVID-19 and it committed to continue to distribute 100% of its proceeds through grants to bars and restaurant workers across the country.
The company's depletions increased 48% in the first quarter and we achieved double-digit volume growth for the 12th consecutive quarter.
In the first quarter in measured off-premise channels, the Truly brand outgrew the hard seltzer category by nearly 2 times or 50 percentage points, resulting in a share increase of 6.5 percentage points.
The Truly brand has now reached a market share of over 28%, accounting for approximately 40% of all growth cases in the hard seltzer category year-to-date, which is two times greater than the next largest growth brand.
Truly Iced Tea Hard Seltzer has achieved a 4.3 percentage point market share in measured off-premise channels, well ahead of all other new entrants to the entire beer category.
Based on information in-hand, year-to-date depletions reported in the company through the 15 weeks ended April 10, 2021, our estimated depletion is approximately 49% from the comparable weeks in 2020.
For the first quarter, we reported net income of $65.6 million or $5.26 per diluted share, an increase of $3.77 per diluted share in the first quarter of last year.
In the first quarter of 2020, we recorded pre-tax COVID-19-related reduction in net revenue and increases in costs, that total $10 million or $0.60 per diluted share.
For the first quarter of 2021, shipment volume was approximately 2.3 million barrels, a 60.1% increase from the first quarter of 2020.
Shipment volume for the quarter was significantly higher than depletions volume and resulted in significantly higher distributor inventory as of March 27, 2021 when compared to March, 28 2020.
Our first quarter 2021 gross margin of 45.8% increase in the 44.8% margin realized in the first quarter of last year.
First quarter advertising, promotional and selling expenses increased by $43 million in the first quarter of 2020, primarily due to increased brand investment of $21 million, mainly driven by higher media and production costs.
Higher salaries and benefits costs and increased freight to distributors of $21.9 million due to a higher volume and rate.
General and administrative expenses increased by $4.9 million from the first quarter of 2020, primarily due to increases in salaries and benefits costs.
During the first quarter, we recorded an income tax expense of $11 million, which consists of income tax expenses of $19.6 million partially offset by $8.6 million fixed benefit related to stock option exercises in accordance with ASU 2016-09.
The effective tax rate for the first quarter, excluding the impact of ASU 2016-09 increased to 25.6% and was 23.6% in the first quarter of 2020.
Based on information of which we are currently aware, we are targeting 2021 earnings per diluted share of between $22 and $26, an increase from the previously communicated range of between $20 and $24, excluding the impact of ASU 2016-09, but actual results could vary significantly from our target.
We are currently planning increases in shipments and depletions of between 40% and 50%, an increase from the previously communicated range of between 35% and 45%.
We're targeting national price increases per barrel of between 1% and 3%, an increase from the previously communicated range of between 1% and 2%.
Full year 2021 gross margins are currently expected to be between 45% and 47%.
We plan increased investments in advertising, promotional and selling expenses of between $130 million to $150 million for the full year 2021, an increase from the previously communicated range of between $120 million and $130 million.
We estimate our full year 2021 effective tax rate to be approximately 26.5% excluding the impact of a ASU 2016-09.
We're not able to provide forward guidance on the impact of ASU 2016-09 [Indecipherable] 2021 financial statements and full year effective tax rate as this will mainly depend upon unpredictable future events, including the timing and value realized upon the exercise of stock options versus the fair value with those options were granted.
We're continuing to evaluate 2021capital expenditures and currently estimate investments of between $250 million and $350 million, a decrease in our previously communicated range of between $300 million and $400 million.
We expect that our March 27, 2021 cash balance of $144.7 million together with the future operating cash flows and the $150 million remaining under the line of credit, will be sufficient to fund future cash requirements.

Summary:
For the first quarter, we reported net income of $65.6 million or $5.26 per diluted share, an increase of $3.77 per diluted share in the first quarter of last year.