Intermittent Fasting Calculator: Find Your Eating Window
Intermittent fasting means eating during a set window of time each day and fasting the rest. It isn’t about what you eat as much as when you eat.
This free intermittent fasting calculator shows your eating window and fasting hours for the most popular plans, based on when you’d like your first meal. No sign-up, and nothing you enter is saved.
Intermittent Fasting Calculator
Pick a fasting plan and when you want your first meal. We’ll show your eating window and a simple daily schedule.
Intermittent Fasting Calculator: Popular Schedules
| Plan | Fasting | Eating window | Example |
|---|---|---|---|
| 12:12 | 12 hours | 12 hours | 7 AM to 7 PM. Many people already do this |
| 14:10 | 14 hours | 10 hours | 9 AM to 7 PM |
| 16:8 | 16 hours | 8 hours | 11 AM to 7 PM |
| 18:6 | 18 hours | 6 hours | 12 PM to 6 PM |
Most of the fasting time happens while you sleep, so a 14:10 plan often just means skipping late-night snacks and having breakfast a little later.
How to Start (Especially After 40)
Use the intermittent fasting calculator above to plan each step:
- Start with 12:12 for a week. Simply stop eating after dinner.
- Move to 14:10 when that feels easy.
- Try 16:8 only if you feel well, sleep well and have steady energy.
- Keep the same window most days. Consistency matters more than the exact hours.
There’s no need to go longer to see a benefit. Many women find 14:10 easier to keep up long term.
Intermittent Fasting Schedule Examples
| Your day | 14:10 eating window | 16:8 eating window |
|---|---|---|
| Early riser (up at 5 or 6 AM) | 7 AM to 5 PM | 8 AM to 4 PM |
| Office hours (up at 7 AM) | 9 AM to 7 PM | 10 AM to 6 PM |
| Late dinners | 10 AM to 8 PM | 12 PM to 8 PM |
| Night owl (up at 9 AM) | 11 AM to 9 PM | 1 PM to 9 PM |
Pick the window that lets you eat dinner with your family and still stop eating 2 to 3 hours before bed. Sleeping well matters more than squeezing in extra fasting hours.
A 3-Week Plan to Work Up to 16:8
| Week | Schedule | Tip |
|---|---|---|
| Week 1 | 12:12 (for example 7 AM to 7 PM) | Just stop snacking after dinner |
| Week 2 | 14:10 (for example 9 AM to 7 PM) | Have black coffee or tea in the morning |
| Week 3 | 16:8 (for example 11 AM to 7 PM), if you feel well | Make your first meal high in protein |
If you feel dizzy, shaky, very tired or can’t sleep, go back to the last schedule that felt good.
What Can You Have While Fasting?
- Water (plain or sparkling)
- Black coffee
- Plain tea, including herbal tea
Anything with calories (milk, cream, sugar, juice) breaks the fast.
More detail: does black coffee break a fast?
What to Eat in Your Eating Window
Intermittent fasting works best with balanced meals:
- Protein at every meal, especially your first one. It helps protect muscle, which matters more after 40. Find your target with our protein calculator.
- Fiber: vegetables, fruit, beans and whole grains help you stay full.
- Healthy fats: olive oil, nuts, seeds and avocado.
- Enough water through the day. Check your needs with the water intake calculator.
Does Intermittent Fasting Work for Weight Loss?
Studies show intermittent fasting can help some people lose weight, mostly because a shorter eating window makes it easier to eat a little less. When total calories are the same, results are often similar to regular calorie cutting. The best plan is the one you can stick to. In menopause and not seeing results? Read why intermittent fasting may not be working.
If weight loss is your goal, set a realistic target with our calorie calculator and see how long it may take with the weight loss timeline calculator.
Who Should Not Try Intermittent Fasting
Talk to your doctor first, or skip it, if you:
- Are pregnant or breastfeeding
- Have diabetes, or take insulin or blood sugar medicine
- Have had an eating disorder
- Take medicines that must be taken with food
- Are under 18
- Have a health condition that affects your blood pressure or blood sugar
Stop and talk to your doctor if you feel dizzy, weak, very tired, or notice your sleep or mood getting worse.
Frequently Asked Questions
What is the best intermittent fasting schedule for women over 40?
Many women do well starting with 12:12 or 14:10. Move to 16:8 only if it feels good and doesn’t hurt your sleep or energy.
Can I drink coffee while fasting?
Yes, black coffee and plain tea are fine. Adding milk, cream or sugar breaks the fast.
Is it OK to fast every day?
Many people follow the same eating window every day. Others fast only on some days. Choose what fits your life.
Does fasting help with menopause belly fat?
Fasting may help with overall weight loss, which can reduce belly fat. Strength training, protein, sleep and stress management matter just as much.
Does intermittent fasting work for women over 50?
It can. Studies so far show weight loss similar to regular calorie cutting, mainly because a shorter eating window helps you eat less. Pair it with enough protein and strength training to protect muscle.
Is 14:10 fasting enough to lose weight?
It can be, if it helps you eat fewer calories overall. Many women find 14:10 easier to keep up than 16:8, and sticking with it matters most. Check your numbers with the calorie deficit calculator.
Should I take my medications while fasting?
Ask your doctor or pharmacist first, especially for diabetes or blood pressure medicines, which may need timing changes.
Related Tools
- Calorie Calculator for Women Over 40
- Protein Calculator for Women Over 40
- Macro Calculator for Women
- Water Intake Calculator
- All free tools
This calculator is for general information only and is not medical advice. Talk to your doctor before changing how you eat if you have a health condition or take medicine. Read our Medical Disclaimer and Editorial Policy.
Sources
- Johns Hopkins Medicine: Intermittent Fasting, What Is It, and How Does It Work? — https://www.hopkinsmedicine.org/health/wellness-and-prevention/intermittent-fasting-what-is-it-and-how-does-it-work
- Dietary Guidelines for Americans — https://www.dietaryguidelines.gov/