Hair grows at approximately 1 cm per month (0.35mm per day), and treatment-driven regrowth follows the same biological timeline with visible results appearing at 4 to 6 months. Understanding your personal regrowth velocity transforms vague expectations into concrete predictions. Instead of wondering "is this working yet?", you can measure exactly how many new hairs are emerging, how fast they are growing, and when you will reach your density target.
This article is for informational purposes only and does not constitute medical advice. Consult a healthcare professional before starting or changing any treatment.
What Regrowth Velocity Actually Measures
Regrowth velocity has two components that are often confused.
Component 1: Linear Growth Rate (How Fast Each Hair Grows)
This is the biological speed at which an individual hair shaft extends from the follicle. For scalp hair, the average is approximately 1 cm per month, though this varies:
- Asian hair: ~1.3 cm per month (fastest average)
- Caucasian hair: ~1.0 cm per month
- African hair: ~0.8 cm per month
Treatment does not significantly change linear growth rate. Finasteride, minoxidil, and PRP do not make individual hairs grow faster. They work by recruiting more follicles into the growth phase and extending the duration of that phase.
Component 2: Follicle Recruitment Rate (How Many New Hairs Appear)
This is the treatment-responsive metric. When a treatment works, dormant or miniaturized follicles begin producing new terminal hairs. The rate at which new hairs appear in your tracking zones is the true measure of treatment velocity.
A fast responder might see 3 to 5 new hairs per cm² per month appearing in the crown. A slow responder might see 0.5 to 1 new hair per cm² per month. Both grow at the same linear rate once they start.
How to Measure Regrowth Velocity
Step 1: Identify New Growth (Baseline Required)
New treatment-driven growth is identifiable in tracking photos by:
- Tapered tips: New hairs have fine, pointed tips. Existing hairs that have been cut or broken have blunt ends.
- Shorter length: New hairs will be noticeably shorter than surrounding mature hairs.
- Emerging in thin areas: New growth appears in areas that were previously lacking density.
- Progressive pigmentation: Early regrowth may appear lighter or finer, darkening as the follicle produces a fuller shaft.
You need a pre-treatment baseline to distinguish new growth from existing hair. Without a baseline, you cannot determine what is new.
Step 2: Measure Linear Growth Rate (Monthly)
Select 5 to 10 identifiable new hairs in your tracking photos. At each monthly photo session:
- Identify the same hairs (use scalp landmarks or reference marks)
- Estimate their length relative to a known reference (ruler, fingertip width)
- Calculate growth per month
If new hairs are 0.5 cm at month 3 and 1.5 cm at month 4, your linear growth rate is 1 cm/month (normal).
Linear growth rate reference:
| Rate | Classification | What It Means |
|---|---|---|
| Above 1.2 cm/month | Fast | Strong follicle health, good blood supply |
| 0.8 to 1.2 cm/month | Normal | Expected range for most people |
| 0.5 to 0.8 cm/month | Slow | May indicate nutritional deficiency or suboptimal follicle health |
| Below 0.5 cm/month | Very slow | Investigate underlying health factors, discuss with doctor |
Step 3: Calculate Follicle Recruitment Rate (Monthly)
Count the number of new short hairs in a defined tracking area at each photo session. The change in count between sessions gives your recruitment rate.
For reliable measurement, use the same 1 cm² area each time. AI tracking tools can automate this by counting hairs below a certain length threshold that were not present in previous images.
Recruitment rate reference:
| Rate (new hairs/cm²/month) | Response Level | Interpretation |
|---|---|---|
| 3 to 5+ | Strong responder | Excellent treatment response |
| 1.5 to 3 | Moderate responder | Good response, results will be visible at 6 to 9 months |
| 0.5 to 1.5 | Slow responder | Detectable response, full results at 12 to 18 months |
| Below 0.5 | Minimal responder | Consider treatment adjustment or addition |
Using Velocity Data to Predict Results
With both metrics in hand, you can build a timeline to your density goal. For context on what density numbers mean, see understanding hair density metrics.
The Prediction Formula
Time to target density = (Target density - Current density) / Recruitment rate
Time to visual impact = Time to target density + (Minimum visible length / Linear growth rate)
Example Calculation
Current crown density: 70 hairs/cm² Target crown density: 90 hairs/cm² Measured recruitment rate: 2 new hairs/cm² per month Linear growth rate: 1 cm per month Minimum visible length: 3 cm
Time to target density: (90 - 70) / 2 = 10 months Time to full visual impact: 10 + (3 / 1) = 13 months
This patient can expect to reach their density target at approximately 10 months, with the newest hairs reaching visible length by month 13.
Why Predictions Have a Range
This calculation assumes a constant recruitment rate, which is an oversimplification. In practice:
- Recruitment rate is highest in the first 6 to 12 months and then slows
- Some recruited follicles may not survive to produce lasting terminal hairs
- Seasonal shedding cycles can temporarily reduce apparent density
- Concurrent treatments (adding minoxidil, PRP) can boost recruitment rate mid-treatment
Treat the prediction as a best-estimate range (plus or minus 3 months) rather than a fixed date.
Velocity as an Early Warning System
Regrowth velocity tracking is not just for measuring progress. It also serves as an early warning system for treatment failure or disease progression.
Declining Velocity
If your recruitment rate drops to zero or your linear growth rate slows significantly, investigate:
- Treatment compliance (missed doses?)
- New health factors (stress, nutritional changes, illness)
- Disease progression outpacing treatment (may need to add a second therapy)
- Medication tolerance (rare, but possible with long-term use)
Velocity Comparison Across Treatments
If you change treatments, velocity tracking lets you compare their effectiveness directly.
For example, if minoxidil alone produced a recruitment rate of 1.5 hairs/cm²/month, and adding finasteride increases it to 2.5 hairs/cm²/month, you have quantified the added value of the second treatment. For detailed minoxidil clinical evidence, the response rates align with these tracking-based observations.
Factors That Affect Regrowth Velocity
Several variables influence how fast you see results:
- Age: Younger patients typically show faster recruitment
- Duration of hair loss: Follicles dormant for less than 5 years respond better
- Norwood stage: Lower stages (2 to 3) show faster velocity than advanced stages (5 to 7)
- Treatment combination: Multi-treatment approaches produce faster recruitment than single agents
- Scalp health: Good circulation, low inflammation, and adequate nutrition support faster growth
- Genetics: Individual variation in follicle sensitivity and growth phase duration
Track Velocity, Set Expectations
Regrowth velocity is the metric that connects your daily treatment routine to a concrete, predictable outcome. It answers the question everyone starting treatment asks: "How long until I see results?" Instead of relying on generic timelines, measure your own.
Start measuring your regrowth velocity today. Upload your photos at myhairline.ai/analyze to get AI-powered density, diameter, and growth tracking that turns your treatment into a data-driven process.
This article is for informational purposes only and does not constitute medical advice. Always consult a qualified healthcare professional before starting, changing, or stopping any treatment.