What this calculator does
A date and time calculator answers a slightly different question from a plain date calculator: instead of shifting a date by whole days, it shifts an exact moment, a specific date and clock time together, by a mix of days, hours and minutes in one combined step.
That combination matters whenever the offset itself is not a clean number of days, such as "72 hours and 30 minutes from now" or "3 days and 6 hours from this departure time". Enter a starting date and time, choose to add or subtract, and fill in any mix of days, hours and minutes; the calculator resolves them together into a single resulting date and time.
The formula
The starting date and time are combined into one moment. The days, hours and minutes entered are converted to a single count of minutes, then added to or subtracted from that moment, with any overflow carrying across hour and day boundaries automatically, including into the next month or year where needed.
| Term | Meaning |
|---|---|
| Starting moment | The combination of the starting date and starting time, treated as a single point in time. |
| Combined offset | The days, hours and minutes entered, added together as one span rather than applied separately. |
| Resulting date and time | The starting moment shifted by the combined offset, in the direction chosen. |
The inputs explained
| Field | What to enter |
|---|---|
| Starting date | The starting calendar date. |
| Starting time | The starting clock time, on the starting date. |
| Direction | Whether the offset below is added to, or subtracted from, the starting date and time. |
| Days | Whole days to include in the offset. Leave at 0 to work in hours and minutes only. |
| Hours | Hours to include in the offset. |
| Minutes | Minutes to include in the offset. |
When to use it
Working out an arrival time after a long journey
A flight, drive or shift that runs a mixed number of days and hours needs the departure date and time shifted by that whole span together, not by days and hours worked out separately and then added back up.
Setting a deadline stated as hours from a specific moment
Terms such as "within 48 hours of dispatch" or "72 hours before the event" start from an exact date and time, not just a date, so the calculator needs a starting time as well as a starting date.
Checking what moment was a mixed offset before now
Log timestamps, incident reports and audit trails sometimes need a moment worked out backward by days, hours and minutes from a known reference point.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
What date and time results from a mixed offset added to a fixed start?
The same starting date and time, with different combined offsets added forward.
| Days added (plus 6 h 30 m each time) | Resulting date and time |
|---|---|
| 0 d | 13 Aug 2026 at 15:30 |
| 1 d | 14 Aug 2026 at 15:30 |
| 2 d | 15 Aug 2026 at 15:30 |
| 3 d | 16 Aug 2026 at 15:30 |
| 5 d | 18 Aug 2026 at 15:30 |
| 7 d | 20 Aug 2026 at 15:30 |
Questions
How is this different from a plain date calculator?
A date calculator such as the date calculator shifts a date by whole days, weeks, months or years and has no concept of a clock time. This tool starts from an exact date and time and can shift it by hours and minutes as well as days, all in one combined step.
Can I add days and hours at the same time?
Yes, that is the main purpose of this calculator. Enter a value in any or all of days, hours and minutes, and they are combined into a single offset before being applied.
What happens if the resulting time crosses midnight?
The date rolls forward or back automatically. Adding 20 hours to 9:00pm, for example, lands on 5:00pm the following day, and the resulting date shown reflects that correctly.
Can I subtract instead of add?
Yes, switch the direction field to Subtract and the same combined offset is taken away from the starting date and time instead of added to it.
For a date-only shift by days, weeks, months or years, use the date calculator. For hours and minutes between two clock times on the same day, see the hours calculator.