Dates and Time Concepts

Add Days

Date intervals add or subtract calendar amounts from a date.

interval `DateInterval` describes the change, and `add` returns the adjusted date.

Add Days

days
add_days.php
Replay: real traced execution (multi-file project)
<?php
$days = 7;
$start = new DateTimeImmutable("2026-05-31", new DateTimeZone("UTC"));
$end = $start->add(new DateInterval("P" . $days . "D"));

echo "days=" . $days . "\n";
echo "end=" . $end->format("Y-m-d") . "\n";

<?php
$days = 1;
$start = new DateTimeImmutable("2026-05-31", new DateTimeZone("UTC"));
$end = $start->add(new DateInterval("P" . $days . "D"));

echo "days=" . $days . "\n";
echo "end=" . $end->format("Y-m-d") . "\n";

<?php
$days = 30;
$start = new DateTimeImmutable("2026-05-31", new DateTimeZone("UTC"));
$end = $start->add(new DateInterval("P" . $days . "D"));

echo "days=" . $days . "\n";
echo "end=" . $end->format("Y-m-d") . "\n";

  1. $days ← 7, $start ← DateTimeImmutable, $end ← DateTimeImmutable

    1<?php2$days→ 7 = 7; //@days=1, 303$start→ DateTimeImmutable = new DateTimeImmutable("2026-05-31", new DateTimeZone("UTC"));4$end→ DateTimeImmutable = $startDateTimeImmutable->add(new DateInterval("P" . $days7 . "D"));56echo "days=" . $days7 . "\n";7echo "end=" . $endDateTimeImmutable->format("Y-m-d") . "\n";
    outputdays=7
end=2026-06-07

  1. $days ← 1, $start ← DateTimeImmutable, $end ← DateTimeImmutable

    1<?php2$days→ 1 = 1;3$start→ DateTimeImmutable = new DateTimeImmutable("2026-05-31", new DateTimeZone("UTC"));4$end→ DateTimeImmutable = $startDateTimeImmutable->add(new DateInterval("P" . $days1 . "D"));56echo "days=" . $days1 . "\n";7echo "end=" . $endDateTimeImmutable->format("Y-m-d") . "\n";
    outputdays=1
end=2026-06-01

  1. $days ← 30, $start ← DateTimeImmutable, $end ← DateTimeImmutable

    1<?php2$days→ 30 = 30;3$start→ DateTimeImmutable = new DateTimeImmutable("2026-05-31", new DateTimeZone("UTC"));4$end→ DateTimeImmutable = $startDateTimeImmutable->add(new DateInterval("P" . $days30 . "D"));56echo "days=" . $days30 . "\n";7echo "end=" . $endDateTimeImmutable->format("Y-m-d") . "\n";
    outputdays=30
end=2026-06-30