# Reverse Time Calculator – When to Start

URL: https://speedycalculator.com/calculators/everyday-life/reverse-time/
Last updated: 2026-10-25

> The reverse time calculator works backwards from a finish time to find when to start – for cooking a meal, getting ready, a journey or a project – adding up several steps and a safety buffer.

## Inputs

- Finish by
- Step 1 (min)
- Step 2 (min)
- Step 3 (min)
- Buffer (min)

## Results

- Total time needed
- Start at
- Start at (24-hour)
- Step 2 starts
- Step 3 starts
- Start day

## Formula

```
Start time = finish time − (step 1 + step 2 + step 3 + buffer)
```

## Explanation

Planning backwards from a fixed deadline – dinner at 7 pm, a flight, an exam – is more reliable than planning forwards. Breaking the job into steps and adding a buffer of 10–20% avoids running late.

### How to use the Reverse Time Calculator – When to Start

- **Finish by**
- **Step 1**
- **Step 2**
- **Step 3**
- **Buffer**

Results update as you type, and every field accepts the units shown in its menu.

### How it works

Pick the time you need to be finished, then enter the length of each step and a buffer.

### Tips

- Check whether the end date should be included – event durations usually include it, elapsed time does not.
- Months have 28–31 days, so "one month" is counted by calendar date, not as 30 days.
- Use 24-hour time or set AM/PM carefully when entering clock times.
- Time zones and daylight-saving changes are not applied unless the calculator says so.

### Common mistakes to avoid

- Counting a 30-day month when a calendar month is meant (or the reverse).
- Forgetting leap years when counting days across February.
- Mixing decimal hours (7.5 h) with clock time (7:30).

### Inputs explained

FieldWhat to enterFinish byA clock time (hours and minutes)Step 1In minStep 2In minStep 3In minBufferIn min

### What each result means

- **Total time needed** = ([Step 1] + [Step 2] + [Step 3] + [Buffer])÷60
- **Start at** = [Finish by] - [Total time needed]
- **Start at (24-hour)** = [Finish by] - [Total time needed]
- **Step 2 starts** = [Finish by] - [Total time needed] + [Step 1]÷60
- **Step 3 starts** = [Finish by] - [Total time needed] + ([Step 1] + [Step 2])÷60

## Worked example

Inputs — Finish by: 19:00; Step 1: 25 min; Step 2: 90 min; Step 3: 15 min; Buffer: 15 min.

Results — Total time needed = 2 h 25 min; **Start at = 4:35 PM**; Start at (24-hour) = 16:35; Step 2 starts = 5:00 PM; Step 3 starts = 6:30 PM; Start day = Same day.

## FAQ

**When should I start cooking to eat at 7 pm?**
Add up prep, cooking and resting time plus a buffer, and subtract it from 7 pm.

**How much buffer should I add?**
About 10–20% of the total, more for travel.

**Can I plan across midnight?**
Yes – the result shows if you need to start the day before.

**What formula does the Reverse Time Calculator – When to Start use?**
Start time = finish time − (step 1 + step 2 + step 3 + buffer).