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# [.NET] 日付計算いろいろ

More than 1 year has passed since last update.

```DateTime date = DateTime.Today;
```

### ▼前月初日

```new DateTime(date.Year, date.Month, 1).AddMonths(-1)
```

### ▼前月同日

```date.AddMonths(-1)
```

### ▼前月末日

```new DateTime(date.Year, date.Month, 1).AddDays(-1)
```

### ▼前々月末日

```new DateTime(date.Year, date.Month, 1).AddMonths(-1).AddDays(-1)
```

### ▼当月初日

```new DateTime(date.Year, date.Month, 1)
```

### ▼当月末日

```new DateTime(date.Year, date.Month, DateTime.DaysInMonth(date.Year, date.Month))
```

### ▼翌月初日

```new DateTime(date.Year, date.Month, 1).AddMonths(1)
```

### ▼翌月末日

```new DateTime(date.Year, date.Month, 1).AddMonths(2).AddDays(-1)
```

### ▼1年前の前月初日

```new DateTime(date.Year, date.Month, 1).AddYears(-1).AddMonths(-1)
```

### ▼1年前の前月末日

```new DateTime(date.Year, date.Month, 1).AddYears(-1).AddDays(-1)
```

### ▼1年前の当月初日

```new DateTime(date.Year, date.Month, 1).AddYears(-1)
```

### ▼4月開始年度

```date.AddMonths(-3).Year
```
【品質と生産性にこだわるシステム開発】 .NET（C#/VB.NET）専門・リモート開発歴10年。即日・1時間から頼める常駐しないエンジニア。確かな技術で開発チームを手堅くサポートします。
https://codeone.jp/
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