Capacitor Aging and End-of-Life Management: Lifespan Calculations, Monitoring, and Replacement Strategies
Last Updated: February 2026 | Reading Time: 15 minutes
Every capacitor has a finite life. Unlike resistors and inductors, which can operate indefinitely under their rated conditions, capacitors undergo irreversible physical and chemical changes that degrade their performance over time. An aluminum electrolytic capacitor loses electrolyte through its seal. A ceramic capacitor's crystal structure slowly shifts, reducing capacitance. A film capacitor accumulates micro-damage from self-healing events. These aging mechanisms are not defects --- they are fundamental material properties. The question is not whether a capacitor will age, but how fast, and what you should do about it.
Understanding capacitor aging is essential for anyone responsible for the long-term reliability of electronic equipment: maintenance engineers managing industrial systems, design engineers selecting components for 15-20 year product lifetimes, and procurement specialists evaluating NOS (new old stock) inventory. This guide covers the aging mechanisms for each capacitor type, life prediction methods, end-of-life indicators, and practical replacement strategies.
Aluminum electrolytic capacitors age primarily through electrolyte evaporation. The liquid or gel electrolyte that forms the cathode contact slowly diffuses through the rubber end seal, reducing the effective contact area between the electrolyte and the dielectric oxide layer.
What changes over time:
- ESR increases (the most sensitive early indicator)
- Capacitance decreases (typically 10-40% loss before functional failure)
- Leakage current may increase (as the oxide layer degrades without electrolyte maintenance)
- Ripple current capability decreases (due to rising ESR and reduced thermal mass)
Rate of aging: Dominated by temperature. The Arrhenius equation (detailed below) governs the evaporation rate. Calendar age also matters --- even unpowered electrolytic capacitors lose electrolyte, though more slowly.
Ceramic capacitors, particularly Class II dielectrics (X7R, X5R, Y5V), exhibit a predictable capacitance decrease over time due to relaxation of the ferroelectric crystal structure. This is sometimes called "aging" or "dielectric aging" and is distinct from the electrolyte-based aging of electrolytics.
What changes over time:
- Capacitance decreases logarithmically with time
- Aging rate is typically 1-5% per decade of time (per decade = per factor-of-10 in hours)
- Class I dielectrics (C0G/NP0) do not exhibit this aging mechanism
Aging rate examples:
| Dielectric | Typical Aging Rate | Capacitance After 10 Years |
|---|
| C0G / NP0 | 0% per decade | No change |
| X7R | 1-2.5% per decade | 94-97% of initial |
| X5R | 3-5% per decade | 88-94% of initial |
| Y5V | 5-7% per decade | 82-88% of initial |
Reversibility: Unlike electrolytic aging, ceramic aging is reversible. Heating the capacitor above its Curie temperature (approximately 125 degrees C for BaTiO3-based ceramics) resets the crystal structure and restores capacitance to its original value. This is called "de-aging." It happens naturally when the capacitor is soldered to a PCB (reflow temperatures far exceed the Curie point), which is why manufacturers specify capacitance values as measured after reflow and 24-hour de-aging.
Metallized film capacitors have a unique aging mechanism: self-healing. When a microscopic dielectric defect causes a localized breakdown, the arc energy vaporizes the thin metallization around the defect, isolating it from the circuit. This is a beneficial failure mode --- it prevents a catastrophic short --- but each self-healing event permanently removes a small area of electrode, slightly reducing capacitance.
What changes over time:
- Capacitance gradually decreases (typically < 3% over operational life)
- Self-healing events are more frequent in humid environments or at higher voltages
- Eventually, accumulated self-healing can reduce capacitance below acceptable limits (graceful end-of-life)
Film capacitors are the longest-lived type. With proper derating, metallized polypropylene film capacitors can operate for 20-30+ years in industrial environments. They have no electrolyte to evaporate and no ferroelectric aging mechanism.
Tantalum capacitors age through gradual degradation of the tantalum pentoxide (Ta2O5) dielectric. Unlike aluminum electrolytics, tantalum capacitors do not have a liquid electrolyte (solid tantalum types use manganese dioxide or conductive polymer as the cathode). Their primary aging mechanism is oxygen vacancy migration in the dielectric under DC bias, which gradually reduces the breakdown voltage margin.
What changes over time:
- Leakage current may increase
- DC breakdown voltage margin decreases
- Catastrophic failure risk increases with age and temperature
- Capacitance remains relatively stable (unlike electrolytics)
Tantalum capacitors age more gracefully than electrolytics in terms of parametric drift but fail more violently when they do fail --- short-circuit failures in solid tantalum capacitors can cause ignition of the MnO2 cathode, producing small but intense fires.
The most important relationship in capacitor life prediction is the Arrhenius equation applied to electrolyte evaporation:
L_actual = L_rated * 2^((T_rated - T_actual) / 10)
Where:
L_actual = predicted life at actual operating temperature
L_rated = manufacturer's rated life at maximum rated temperature
T_rated = maximum rated temperature (85 or 105 degrees C)
T_actual = actual core temperature during operation
This is commonly called the "10 degree C rule": for every 10 degrees C reduction in operating temperature below the rated maximum, capacitor life doubles. Conversely, every 10 degrees C increase halves the life.
Example 1: Standard industrial capacitor
A Nichicon LGU series capacitor rated 2,000 hours at 105 degrees C, operating in a VFD at an internal temperature of 65 degrees C:
L = 2,000 * 2^((105 - 65) / 10)
L = 2,000 * 2^4
L = 2,000 * 16
L = 32,000 hours
L = 3.65 years of continuous operation
At 8 hours/day, 250 days/year operation:
L_calendar = 32,000 / (8 * 250) = 16 years
Example 2: Long-life capacitor in cooler environment
A Nippon Chemi-Con KMR series capacitor rated 10,000 hours at 105 degrees C, operating in a UPS room at 45 degrees C:
L = 10,000 * 2^((105 - 45) / 10)
L = 10,000 * 2^6
L = 10,000 * 64
L = 640,000 hours
L = 73 years of continuous operation
Example 3: Undersized capacitor in hot environment
A standard 85 degree C capacitor rated 2,000 hours, operating at 80 degrees C (only 5 degrees below maximum):
L = 2,000 * 2^((85 - 80) / 10)
L = 2,000 * 2^0.5
L = 2,000 * 1.41
L = 2,828 hours
L = 0.32 years (about 4 months) of continuous operation
This is why an 85 degree C capacitor in a hot environment fails in months, not years.
The 10 degree C rule is an approximation. Real-world factors that cause actual life to differ from the prediction:
- Ripple current heating: The Arrhenius equation uses core temperature, not ambient temperature. Ripple current adds internal heating (delta T = I_ripple^2 * ESR * R_thermal). Some manufacturers provide life equations that include ripple current correction.
- Voltage stress: Higher voltage stress accelerates oxide degradation independently of temperature. Some manufacturers include a voltage acceleration factor: L = L_rated * 2^((T_rated - T_actual)/10) * (V_rated / V_actual)^n, where n is typically 2-5.
- Humidity: High humidity accelerates corrosion of lead wires and end seals, which is not captured by the temperature model.
- Duty cycle: The model assumes continuous operation. Equipment that cycles on and off may have different thermal profiles and electrolyte evaporation patterns.
Despite these limitations, the Arrhenius model is the standard tool for capacitor life prediction and is accurate within a factor of 2 for most applications --- sufficient for maintenance planning.
| Parameter | Threshold for Concern | Threshold for Replacement | Measurement Method |
|---|
| ESR | > 1.5x rated value | > 2x rated value | ESR meter at 100 kHz |
| Capacitance | < 90% of rated value | < 80% of rated value | LCR meter at rated frequency |
| Leakage current | > 2x rated value | > 5x rated value | DC voltage applied, measure current after 5 min |
| Ripple voltage | 50% increase over baseline | 100% increase (doubled) | Oscilloscope on DC bus |
| Dissipation factor | > 1.5x rated value | > 2x rated value | LCR meter |
ESR is the most sensitive indicator. In most aging electrolytic capacitors, ESR rises significantly before capacitance drops measurably. An ESR test program that measures periodically and tracks trends will detect degradation months to years before functional failure. See our Advanced Capacitor Testing guide for detailed measurement techniques.
- Bulging vent: The pressure relief vent on top of the capacitor is bowed outward. This indicates internal gas buildup from electrolyte decomposition --- the capacitor is at or past its end of life.
- Electrolyte leakage: Brown, crusty, or oily residue at the base of the capacitor or on the PCB beneath it. The end seal has failed, and electrolyte is escaping.
- Discoloration of the sleeve: The PVC or rubber sleeve has darkened, shrunk, or cracked from heat exposure. This indicates the capacitor has been operating near its thermal limits.
- Corrosion on terminals: Green or white deposits on the capacitor leads or solder joints. Common in humid environments and indicates accelerated aging.
Any visible abnormality warrants immediate ESR testing. A capacitor that looks damaged may still be within specification, but visual changes always indicate stress that accelerates aging.
Many industrial facilities use calendar-based replacement schedules for electrolytic capacitors in critical equipment:
| Equipment Type | Typical Replacement Interval | Basis |
|---|
| UPS systems | 5-7 years | Manufacturer recommendation |
| VFDs (variable frequency drives) | 7-10 years | Based on Arrhenius life at typical ambient |
| Power supplies (telecom, data center) | 7-10 years | Carrier and OEM guidelines |
| Medical equipment | 5-7 years | Regulatory and liability requirements |
| Industrial controls (PLC power supplies) | 10-15 years | Typically replaced when other components fail |
Advantages: Simple to schedule and budget. Prevents catastrophic in-service failures. Does not require test equipment or skilled personnel for condition assessment.
Disadvantages: Replaces many capacitors that still have useful life remaining (wasteful and expensive). Does not catch early failures (infant mortality). The replacement interval is a guess based on average conditions, not actual operating conditions.
Condition-based maintenance (CBM) monitors the actual health of capacitors and replaces them when degradation indicates approaching end of life. This approach is more cost-effective for large installed bases:
Implementation steps:
-
Baseline measurement: When equipment is installed or capacitors are replaced, measure and record ESR and capacitance of each capacitor (or at least the most critical ones --- DC bus capacitors in drives, bulk capacitors in power supplies).
-
Periodic monitoring: Measure the same parameters on a regular schedule (annually for most industrial equipment, semi-annually for critical systems). Record results in a maintenance database.
-
Trend analysis: Plot ESR and capacitance over time. Healthy capacitors show slow, linear degradation. Capacitors approaching end of life show accelerating ESR rise.
-
Threshold-based replacement: Schedule replacement when ESR exceeds 2x the baseline value or capacitance drops below 85% of baseline. This typically gives 6-12 months of lead time before functional failure.
Advantages: Replaces capacitors based on actual condition, not arbitrary calendar intervals. Catches early failures that time-based schedules miss. More cost-effective for large installations.
Disadvantages: Requires test equipment (ESR meters or LCR meters), trained personnel, and a data tracking system. Initial measurement effort is significant.
Many organizations combine both approaches: time-based replacement for the most critical capacitors (UPS DC bus, life-safety systems) and condition-based monitoring for less critical systems (general-purpose VFDs, non-critical power supplies). This balances cost against risk.
NOS capacitors --- new capacitors that have been stored for years or decades without being used --- present a unique aging challenge. The capacitor has never been electrically stressed, but its materials have aged:
Step 1: Visual inspection. Check for bulging, leaking, corroded terminals, and damaged sleeves. Any visible damage disqualifies the capacitor.
Step 2: Measure leakage current. Apply rated voltage through a current-limiting resistor (1-10 kohm) and monitor leakage current. A new electrolytic capacitor should have leakage current below I_leakage = 0.01 * C * V + 3 (microamps, for C in uF and V in volts). NOS capacitors may have much higher initial leakage due to oxide layer degradation during storage.
Step 3: Reform the capacitor. Gradually increase applied voltage over several hours while monitoring leakage current. This rebuilds the aluminum oxide dielectric layer. See our Capacitor Reforming Guide for detailed procedures.
Step 4: Measure capacitance and ESR. After reforming, measure these parameters and compare to the manufacturer's original specifications. Capacitance should be within the tolerance band. ESR should be close to the original specification (within 50%).
Step 5: Evaluate the electrolyte condition. Even after successful reforming, a capacitor stored for 15-20+ years may have lost significant electrolyte volume. The capacitor may meet specifications initially but degrade faster than expected because the electrolyte reservoir is already partially depleted. For critical applications, NOS electrolytic capacitors older than 10-15 years should be treated as limited-life components with more frequent monitoring.
For detailed guidance on capacitor storage considerations, see our Capacitor Shelf Life Guide.
Operating a capacitor at a fraction of its rated voltage significantly extends life:
- For electrolytic capacitors, operating at 80% of rated voltage can double the expected life
- At 60% of rated voltage, life may increase by 4-8x
- The voltage acceleration factor varies by manufacturer and series
See our Capacitor Derating Guide for specific recommendations by capacitor type.
Since temperature is the dominant aging factor for electrolytic capacitors, every degree of temperature reduction pays dividends:
- Position electrolytics away from heat sources (power transistors, braking resistors, transformers)
- Ensure adequate airflow --- blocked fan filters are a common cause of accelerated capacitor aging in VFDs and power supplies
- Orient capacitors vertically if possible, so hot air rises away from the capacitor body rather than bathing it
- Use thermal barriers (insulating washers, air gaps) between hot chassis surfaces and capacitor mounting locations
- Specify 105 degree C capacitors instead of 85 degree C for any application where ambient temperature exceeds 40 degrees C or internal equipment temperature exceeds 60 degrees C
Capacitor manufacturers offer series with rated lifetimes ranging from 1,000 to 20,000+ hours at maximum rated temperature. The longer-life series use improved sealing materials, more stable electrolytes, and tighter manufacturing tolerances.
Example life comparison for a 470 uF, 400V capacitor at 65 degrees C ambient:
| Capacitor Series | Rated Life at 105 C | Calculated Life at 65 C | Calendar Years (24/7) |
|---|
| Economy (2,000 hr) | 2,000 hours | 32,000 hours | 3.7 years |
| Standard (5,000 hr) | 5,000 hours | 80,000 hours | 9.1 years |
| Long-life (10,000 hr) | 10,000 hours | 160,000 hours | 18.3 years |
| Ultra-long-life (20,000 hr) | 20,000 hours | 320,000 hours | 36.5 years |
The cost difference between economy and long-life series is typically 30-80%. The life difference is 5x. For industrial equipment expected to operate for 15-20 years, specifying long-life capacitors at the design stage is far less expensive than field replacement.
For the most critical applications, design the circuit to function with n-1 capacitors in a parallel bank of n. If one capacitor fails open or is removed for replacement, the system continues to operate (with increased ripple) until the replacement is installed. This is common practice in UPS systems and telecom power plants.
In well-designed equipment operating at moderate temperatures (40-60 degrees C ambient), quality electrolytic capacitors typically last 10-20 years. The actual life depends on the capacitor's rated life at maximum temperature, the actual operating temperature (including self-heating from ripple current), and the voltage stress. Using the Arrhenius equation with measured or estimated operating temperatures gives a reasonable prediction. In hot environments (industrial cabinets above 50 degrees C, poorly ventilated enclosures), life can be as short as 3-7 years. In cool, climate-controlled environments (data centers, telecom rooms at 20-25 degrees C), life can exceed 25 years.
Ceramic capacitors do not wear out in the same way as electrolytics --- there is no electrolyte to evaporate. However, Class II ceramics (X7R, X5R, Y5V) exhibit logarithmic capacitance aging of 1-7% per decade of time due to ferroelectric crystal relaxation. This aging is reversible if the capacitor is heated above its Curie temperature. In practice, ceramic capacitor aging is rarely a reliability concern because the total capacitance loss over a 20-year period is typically less than the initial tolerance. Ceramic capacitors fail primarily from mechanical stress (flex cracking), not parametric aging.
Preventive replacement is justified when the cost of unplanned downtime significantly exceeds the cost of replacement. This includes UPS systems protecting critical loads, VFDs on production lines where downtime costs exceed thousands of dollars per hour, medical equipment where failure has patient safety implications, and telecom infrastructure where service level agreements impose penalties. For non-critical equipment (bench power supplies, non-essential HVAC), run-to-failure is often more cost-effective if spare parts and repair capability are available. The break-even calculation is: if (cost_of_downtime * probability_of_failure) > cost_of_preventive_replacement, then replace preventively.
How do I calculate the remaining life of an installed capacitor?#
Estimate the remaining life by combining the Arrhenius prediction with actual condition measurements. First, calculate the total expected life using the Arrhenius equation and the measured or estimated operating temperature. Subtract the time already in service to get the remaining predicted life. Then verify with condition measurements: measure ESR and capacitance, compare to the original specifications, and assess what fraction of the allowable degradation has occurred. If 50% of the life has elapsed and ESR has risen 30% (out of a 100% maximum rise), the two estimates roughly agree. If ESR has risen 80% in only 30% of the predicted life, something is wrong --- the capacitor is aging faster than expected, possibly due to higher-than-estimated temperature, excessive ripple current, or a manufacturing defect.
NOS electrolytic capacitors can be safe to use if they are properly assessed and reformed, but they should be treated as components with reduced remaining life. The electrolyte has been slowly evaporating during storage (even without electrical stress), and the aluminum oxide dielectric has partially degraded. After reforming, measure capacitance and ESR to verify they meet original specifications. If they do, the capacitor is functional but has already consumed some of its electrolyte reserve. For non-critical applications with regular monitoring, NOS electrolytics under 10-15 years old are generally acceptable. For critical applications, new-manufacture capacitors are always preferred. NOS film and ceramic capacitors are less concerning because they have no electrolyte and their aging mechanisms are far less significant.
- Capacitor Shelf Life Guide --- Storage conditions, shelf life by type, and when reforming is required for stored capacitors
- Capacitor Derating Guide --- Voltage and temperature derating recommendations to maximize operational life for every capacitor type
- Capacitor Value Calculator --- Convert capacitor codes and markings when identifying installed components for aging assessment
- Energy Storage Calculator --- Calculate stored energy and discharge time for capacitor safety during replacement procedures
