THE NUMBERS, EXPLAINED
How to use this calculator.
Months are added first, clamping to the last valid day of the target month. Calendar days are then added.
Start with your inputs
Enter start date, months to add, days to add. Keep amounts in the units shown on each field. The example is a starting point, not a recommended value.
| Input | Example value |
|---|---|
| Start date | 2026-01-31 |
| Months to add | 1 |
| Days to add | 0 |
A worked example
With the example inputs above, resulting date is 2026-02-28. Change the inputs to explore your own scenario.
| Result | Example answer |
|---|---|
| Resulting date | 2026-02-28 |
How this is calculated
Resulting date
shiftDate(a,b,c)
Symbols and units
- a
- Start date
- b
- Months to add
- c
- Days to add
Use the units shown. A list keeps the order in which you enter its values. The symbol ^ means “raised to the power of”.
Calculation steps and notation
Move to the requested month, keeping the day of month where possible and clamping to that month’s last day otherwise. Then add the requested number of calendar days, using UTC dates.
Assumptions and limits
Months are added first, clamping to the last valid day of the target month. Calendar days are then added.
Calculations use the values you enter. Blank or invalid inputs show an error instead of silently substituting zero. Results are displayed to useful precision; calculations retain the underlying numeric precision.
Questions about this tool
What does the result tell me?
Resulting date. The result applies to the method and inputs described above. Check the units and assumptions before using it in a decision.
Why might another calculator differ?
Differences in units, rounding, timing or model definitions can produce different answers. Compare the input definitions and the method, rather than only the final number. For this tool: Months are added first, clamping to the last valid day of the target month. Calendar days are then added.
Are my inputs stored or sent to AI?
Calculations on this page happen in your browser. The separate AI question finder sends its submitted conversation to OpenAI; these calculator fields are not sent. Favourites and recent tool names are stored locally. A shared link contains the inputs you choose to include.
Review status
Software example and browser checks are recorded in our quality report. No external expert review is claimed. Created with coding assistance; calculations run as ordinary browser code.
Read the quality report →