Question: ```
$somedate = "1980-02-15";
$otherdate = strtotime('+1 year', strtotime($somedate));
echo date('Y-m-d', $otherdate);

```

outputs

```
1981-02-15

```

and

```
$somedate = "1980-02-15";
$otherdate = strtotime('+2 year', strtotime($somedate));
echo date('Y-m-d', $otherdate); 

```

outputs

```
1982-02-15

```

but

```
$somedate = "1980-02-15";
$otherdate = strtotime('+75 year', strtotime($somedate));
echo date('Y-m-d', $otherdate); 

```

outputs

```
1970-01-01

```

How to fix?

Answer: 
For unix timestamp, the maximum representable time is 2038-01-19. At 03:14:07 UTC.

So you can't represent/operate time that over it by using timestamp.
75 years from 1980 is 2055, which is past the highest date value that can be represented in a 32-bit integer. Therefore the result becomes 0, which is the 1970 date you observe.