What health calculators does Texterfly offer?

Texterfly offers 3 free health calculators: a BMI Calculator (adult and child/teen modes, visual gauge, healthy weight range), a Calorie & Macro Calculator (Mifflin-St Jeor and Katch-McArdle formulas, macronutrient breakdown, goal-based timeline), and a Pregnancy Due Date Calculator (last menstrual period or conception date methods, trimester guide, weekly development milestones). All are for informational purposes only.

What do the BMI categories mean?

BMI (Body Mass Index) categories for adults are: Underweight (below 18.5), Normal weight (18.5–24.9), Overweight (25–29.9), Obese Class I (30–34.9), Obese Class II (35–39.9), and Obese Class III (40 and above). Note that BMI has significant limitations — it does not account for muscle mass, bone density, age, sex, or ethnicity. Athletes may have a high BMI due to muscle, not fat. Always consult a healthcare professional for a full health assessment.

What is the Mifflin-St Jeor formula?

The Mifflin-St Jeor formula estimates Basal Metabolic Rate (BMR) — calories burned at rest. For men: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) + 5. For women: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) − 161. Multiplying BMR by an activity factor gives TDEE (Total Daily Energy Expenditure), which is the estimated number of calories needed to maintain current weight.

TDEE (Total Daily Energy Expenditure) is the estimated total number of calories you burn per day, including physical activity. It is calculated by multiplying your BMR (Basal Metabolic Rate) by an activity factor: Sedentary (×1.2), Lightly active (×1.375), Moderately active (×1.55), Very active (×1.725), Extra active (×1.9). To lose weight, eat fewer calories than your TDEE; to gain, eat more.

How is a pregnancy due date calculated?

The most common method is Naegele's rule: add 280 days (40 weeks) to the first day of your Last Menstrual Period (LMP). For example, if your LMP was January 1, the estimated due date is October 8. Alternatively, add 266 days to a known conception date. Only about 5% of babies are born on their exact due date — it's an estimate within a 2-week window.

What are the pregnancy trimesters?

First Trimester: Weeks 1–12 (months 1–3). Key developments: fertilisation, heart formation, organ development. Second Trimester: Weeks 13–26 (months 4–6). Key developments: movement felt, sex identifiable, rapid growth. Third Trimester: Weeks 27–40+ (months 7–9+). Key developments: lungs mature, weight gain, preparation for birth.

Are these calculators a substitute for medical advice?

No. These calculators are for informational and educational purposes only. They are not designed to diagnose, treat, cure, or prevent any medical condition. BMI, calorie needs, and pregnancy timelines are estimates based on statistical formulas — individual health varies significantly. Always consult a qualified healthcare professional, doctor, or registered dietitian for personalised medical guidance.

How accurate is the BMI calculator?

The BMI formula is mathematically accurate — it correctly calculates weight (kg) divided by height (m²). However, BMI as a health metric has well-documented limitations: it does not distinguish between fat and muscle, does not account for where fat is stored (visceral vs subcutaneous), and may misclassify athletes as overweight and elderly people with muscle loss as normal weight. Use BMI as one data point, not a definitive measure of health.

Are these health calculators free?

Yes. All 3 health calculators are 100% free with no registration, subscription, or payment required.

Is my health data private?

Yes. All calculations run entirely in your browser. Your weight, height, age, activity level, and other personal health data are never sent to any server or stored anywhere.

Why do the splits assume an even pace?

Even splits are the simplest way to plan a target pace and are a common coaching recommendation as a baseline, even though real races often vary somewhat due to terrain, fatigue, or strategy.

Back to Health & Fitness Calculators

Running Pace Calculator

Calculate running pace, finish time, or distance from any two of the three, in min/mile or min/km. Includes splits and a race time predictor. Free, no sign-up.

Training for a race?

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Health & Fitness

Solve For

Pick which value you want calculated — fill in the other two below.

Distance (mi)

Pace (per mi)

Result

Distance

3.11 mi

Time

25:01

Pace

8:03 /mi

Split Times

Mile	Split	Cumulative
1	8:03	8:03
2	8:03	16:06
3	8:03	24:09
3.11	0:52	25:01

Splits assume an even pace throughout — real race pacing (negative/positive splits, terrain, weather) will vary. This tool is for training and planning reference only.

Race Time Predictor

Enter a recent race result and predict your equivalent time at other common distances, using the Riegel formula.

Recent Race Distance

Your Finish Time

hms

Distance	Predicted Time	Pace
1 Mile	7:31	7:31 /mi
5KYOUR RESULT	25:00	8:03 /mi
10K	52:07	8:23 /mi
15K	1:20:07	8:36 /mi
10 Miles	1:26:19	8:38 /mi
Half Marathon	1:55:00	8:46 /mi
Marathon	3:59:47	9:09 /mi

Riegel's formula: T2 = T1 × (D2/D1)^1.06. Most accurate for predictions between 3K and marathon distance, for a similarly-trained effort.

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Free Running Pace Calculator — Pace, Time, Distance & Splits

Give this calculator any two of pace, time, or distance and it solves the third instantly, in miles or kilometers. It also breaks your result down into mile-by-mile or kilometer-by-kilometer split times, and includes a race time predictor that estimates your equivalent finish time at other common distances from a recent result. Everything runs instantly in plain JavaScript, no sign-up required.

The Pace, Time & Distance Relationship

Pace, time, and distance are related by one simple equation: Time = Pace × Distance. Rearranged, that also gives you Pace = Time ÷ Distance and Distance = Time ÷ Pace. Pick whichever one you're trying to find, enter the other two, and the calculator handles the conversion between minutes-per-mile and minutes-per-kilometer for you.

🎯 Plan a goal race time

Know your target finish time and race distance? Solve for pace to find exactly what speed you need to hold.

🏁 Check a training run

Know your pace and how long you ran? Solve for distance to see how far a timed run actually covered.

Using Splits & Race Predictions in Training

⏱️

Even splits are usually the goal

Most coaches recommend running even or slightly negative splits (second half faster than the first) rather than starting too fast — the split table shows what a perfectly even pace looks like for your goal.

📈

Race predictions work best across similar distances

Riegel's formula is most reliable when predicting between a 3K and a marathon effort for a similarly-trained runner — predicting a marathon time from a mile time, for example, is far less reliable.

🌡️

Conditions change everything on race day

Heat, hills, altitude, and course conditions all affect real-world pacing — treat splits and predictions as a planning baseline, not a guarantee.

🔁

Re-run predictions after key workouts

A recent hard effort (a time trial or a race) gives a much more accurate prediction than an old result from months ago as your fitness changes.

🥇

Use splits to practice pacing in training

Running goal-pace intervals using the split table's per-mile or per-km times is one of the most effective ways to build a feel for race pace before the actual event.

Frequently Asked Questions

How do I calculate my pace from a race time?

Set "Solve For" to Pace, enter the race distance and your finish time, and the calculator returns your pace per mile or per kilometer.

How accurate is the race time predictor?

It uses Riegel's formula (T2 = T1 × (D2/D1)^1.06), a widely used and reasonably accurate model for predicting race times across different distances for a similarly-trained effort. It's most reliable between about 3K and marathon distance.

What's the difference between min/mile and min/km pace?

They're the same concept in different units — minutes per mile is standard in the US, while minutes per kilometer is standard almost everywhere else. This calculator converts between them automatically when you switch units.

Why do my splits assume an even pace?

Even splits are the simplest way to plan a target pace and are what most coaches recommend as a baseline strategy — real races often vary slightly due to terrain, fatigue, or strategy, but even splits are a solid planning reference.

Can I use this for kilometers instead of miles?

Yes — toggle the unit switch to km and every distance, pace, and split calculation updates to metric automatically.

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